424B3 1 ea0289249-424b3_citius.htm PROSPECTUS SUPPLEMENT

Prospectus Supplement No. 1 dated May 5, 2026	Filed Pursuant to Rule 424(b)(3)
(to Prospectus dated March 2, 2026)	Registration No. 333-288656

Citius Oncology, Inc.

6,818,182 Shares of Common Stock underlying the Warrants

272,727 Shares of Common Stock Underlying the Placement Agent’s Warrants

This prospectus supplement updates, amends and supplements the prospectus dated March 2, 2026 (as supplemented or amended from time to time, the “Prospectus”), which forms a part of the Post-Effective Amendment to the Registration Statement on Form S-1 (Registration No. 333-288656). Capitalized terms used in this prospectus supplement and not otherwise defined herein have the meanings specified in the Prospectus.

This prospectus supplement is being filed to update, amend and supplement the information included in the Prospectus with the information contained in our Current Reports on Form 8-K filed with the Securities and Exchange Commission on March 4, 2026, March 10, 2026, March 31, 2026, April 28, 2026 and April 29, 2026 (collectively, the “Current Reports”). Accordingly, we have attached the Current Reports and related exhibits to this prospectus supplement.

This prospectus supplement is not complete without the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

Our Common Stock is listed on the Nasdaq Capital Market under the symbol “CTOR.” The last reported closing price for our Common Stock on May 4, 2026, was $0.92 per share.

Investing in our securities involves a high degree of risk, including the risk of losing your entire investment. See “Risk Factors” beginning on page 8 of the Prospectus to read about factors you should consider before investing in our securities.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is May 5, 2026

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) March 4, 2026

Citius Oncology, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

001-41534		99-4362660
(Commission File Number)		(IRS Employer Identification No.)

11 Commerce Drive, 1st Floor, Cranford, NJ		07016
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (908) 967-6677

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock		CTOR		The Nasdaq Capital Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On March 4, 2026, we issued a press release announced positive topline safety and efficacy results from an investigator initiated Phase 1 trial evaluating LYMPHIR™ (E7777, denileukin diftitox cxdl) administered prior to commercial CD19 directed CAR T therapy in patients with high risk relapsed or refractory diffuse large B cell lymphoma (DLBCL). A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press release, dated March 4, 2026.
104		Cover Page Interactive Data File, formatted in Inline Extensible Business Reporting Language (iXBRL).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	CITIUS ONCOLOGY, INC.

Date: March 4, 2026	/s/ Leonard Mazur
	Leonard Mazur
	Chairman and Chief Executive Officer

Exhibit 99.1

Citius Oncology Announces Preliminary Topline Phase 1 Data from Study of LYMPHIR™ (E7777) Dosing Prior to Commercial CAR-T Therapy in High-Risk Diffuse Large B-Cell Lymphoma

Topline data of investigator-initiated study at the University of Minnesota and City of Hope demonstrates 86% overall response rate (OR), including 57% complete response (CR) and 29% partial response (PR)

LYMPHIR was well-tolerated with no dose-limiting toxicities observed

CRANFORD, N.J., March 4, 2026 – Citius Oncology, Inc. (“Citius Oncology”) (Nasdaq: CTOR), an oncology-focused biopharmaceutical company and majority-owned subsidiary of Citius Pharmaceuticals, Inc. (“Citius Pharma”) (Nasdaq: CTXR), today announced positive topline safety and efficacy results from an investigator-initiated Phase 1 trial evaluating LYMPHIR™ (E7777, denileukin diftitox-cxdl) administered prior to commercial CD19-directed CAR-T therapy in patients with high-risk relapsed or refractory diffuse large B-cell lymphoma (DLBCL). The trial was conducted by lead investigator, Dr. Veronika Bachanova, at the University of Minnesota and City of Hope. Full results were presented at the 2026 ASTCT^® & CIBMTR^® Tandem Meetings¹.

The Phase 1 trial was designed to augment the lymphodepletion regimen prior to CAR-T infusion through the administration of LYMPHIR to potentially improve the anti-tumor activity of CAR-T therapies. LYMPHIR, an engineered fusion toxin that preferentially binds to the IL-2 receptor expressed on regulatory T-cells (Tregs), is currently FDA-approved and commercially available for the treatment of relapsed or refractory cutaneous T-cell lymphoma (CTCL) after one prior systemic therapy.

“Enhancing Treg depletion prior to CAR-T infusion with LYMPHIR represents a promising immunomodulatory strategy in patients with high-risk DLBCL, and these Phase 1 data provide an encouraging signal of the potential to enhance current CAR-T regimens,” said Dr. Myron Czuczman, Executive Vice President and Chief Medical Officer of Citius Oncology and Citius Pharma. “These positive data support our broader strategy of exploring LYMPHIR’s modulatory effect on Tregs in combination with other approved therapies to potentially enhance the body’s own immune system to fight cancerous tumors,” he added.

Topline Results & Study Design

●

All patients (n=14) completed treatment and proceeded to CAR-T infusion;

●

LYMPHIR was well tolerated, with no dose-limiting toxicities observed;

●

No Grade ≥3 LYMPHIR-related immune adverse events or infusion reactions were reported; and,

●

Data demonstrated effective Treg depletion, and promising efficacy signals of enhanced standard lymphodepletion with the use of Treg-targeting LYMPHIR.

The Phase 1, open-label, dose-escalation study (NCT04855253), enrolled 14 patients with relapsed or refractory DLBCL exhibiting poor prognostic features, including double/triple hit genetics, primary refractory disease, and extranodal involvement. Participants received one dose of LYMPHIR (E7777) at 5, 7, or 9 µg/kg followed by low dose chemotherapy prior to standard commercial CD19-directed CAR-T cell therapy. All patients received an infusion of one of the following FDA-approved, commercially manufactured CAR-T products: axicabtagene ciloleucel (Yescarta^®; Kite Pharma/Gilead Sciences), lisocabtagene maraleucel (Breyanzi^®; Bristol Myers Squibb), or tisagenlecleucel (Kymriah^®; Novartis).

The use of LYMPHIR in this study was investigational and outside of its FDA-approved indication. The Phase 1 study was not designed or powered to evaluate clinical efficacy, and no conclusions can be drawn regarding comparative effectiveness or long-term outcomes.

Key Findings from the Phase 1 Trial

●

Overall response rate (ORR) was 86% at one month, including 57% complete responses (CR) and 29% partial responses (PR);

●

One-year progression-free survival (PFS) was 77% (95% CI: 43–92%);

●

One-year overall survival (OS) was 84% (95% CI: 49–96%);

●

A single LYMPHIR dose resulted in depletion of circulating Tregs in all but one patient;

Median reduction of 24 Tregs/µL (range 8–65);

Treg nadir was observed 24 hours post-LYMPHIR;

●

LYMPHIR was well tolerated with no dose-limiting toxicities (DLTs) observed up to 9 µg/kg; and,

●

Reported adverse events included manageable Grade 1–2 capillary leak syndrome, fever, and transient liver enzyme elevations; Grade 3 cytopenias were consistent with expected lymphodepletion. CAR-T related cytokine release syndrome (CRS) occurred in 43% of patients (all Grade 1/2), and immune effector cell-associated neurotoxicity syndrome (ICANS) occurred in 21% (primarily low grade).

“In this high-risk population, LYMPHIR showed a favorable safety profile and promising pharmacodynamic effects when administered prior to CAR-T therapies. This data sets the stage for a larger study to assess its potential to enhance CAR-T efficacy through longer duration of LYMPHIR use,” said Dr. Veronika Bachanova, Principal Investigator and Professor of Medicine at the University of Minnesota.

Dr. Bachanova presented the topline data at the 2026 Tandem Meetings | ASTCT^® CIBMTR^®.

Title: E7777 to Enhance Regulatory T-Cell Depletion Prior to CAR-T for High-Risk LBCL

Presentation ID: 677608

Abstract ID: 296369

About Diffuse Large B-Cell Lymphoma (DLBCL)

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma (NHL), accounting for approximately 30%–40% of newly diagnosed cases in the United States. DLBCL is an aggressive and rapidly growing cancer of B lymphocytes, a type of white blood cell responsible for producing antibodies. While frontline chemoimmunotherapy regimens such as R-CHOP can be curative for many patients, up to 40% experience relapse or refractory disease. High-risk features are associated with poor outcomes and limited responses to standard therapies, including CAR-T cell therapy. Novel strategies that modulate the tumor microenvironment, such as transient regulatory T-cell depletion, are under investigation to improve treatment efficacy and long-term remission rates in this difficult-to-treat population.

About LYMPHIR™ (denileukin diftitox-cxdl)

LYMPHIR is a targeted immune therapy for relapsed or refractory cutaneous T-cell lymphoma (CTCL) indicated for use in Stage I-III disease after at least one prior systemic therapy. It is a recombinant fusion protein that combines the IL-2 receptor binding domain with diphtheria toxin (DT) fragments. The agent specifically binds to IL-2 receptors on the cell surface, causing diphtheria toxin fragments that have entered cells to inhibit protein synthesis. After uptake into the cell, the DT fragment is cleaved and the free DT fragments inhibit protein synthesis, resulting in cell death. Denileukin diftitox-cxdl demonstrated the ability to deplete immunosuppressive regulatory T lymphocytes (Tregs) and antitumor activity through a direct cytocidal action on IL-2R-expressing tumors.

In 2021, denileukin diftitox received regulatory approval in Japan for the treatment of relapsed or refractory CTCL and peripheral T-cell lymphoma (PTCL). Subsequently, in 2021, Citius acquired an exclusive license with rights to develop and commercialize denileukin diftitox in all markets except for India, Japan and certain parts of Asia. LYMPHIR (denileukin diftitox-cxdl) was approved by the FDA and subsequently launched in the U.S. in December 2025.

About Citius Oncology, Inc.

Citius Oncology, Inc. (Nasdaq: CTOR) is a platform to develop and commercialize novel targeted oncology therapies. In December 2025, Citius Oncology launched LYMPHIR, approved by the FDA for the treatment of adults with relapsed or refractory Stage I–III CTCL who had had at least one prior systemic therapy. Management estimates the initial market for LYMPHIR currently exceeds $400 million, is growing, and is underserved by existing therapies. Robust intellectual property protections that span orphan drug designation, complex technology, trade secrets and pending patents for immuno-oncology use as a combination therapy with checkpoint inhibitors would further support Citius Oncology’s competitive positioning. For more information, please visit www.citiusonc.com.

Forward-Looking Statements

This press release may contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such statements are made based on our expectations and beliefs concerning future events impacting Citius Oncology. You can identify these statements by the fact that they use words such as “will,” “anticipate,” “estimate,” “expect,” “plan,” “should,” and “may” and other words and terms of similar meaning or use of future dates. Forward-looking statements are based on management’s current expectations and are subject to risks and uncertainties that could negatively affect our business, operating results, financial condition and stock price. Factors that could cause actual results to differ materially from those currently anticipated are: risks relating to the results of research and development activities, including those from our existing and any new pipeline assets; early-stage clinical data may not be predictive of results from larger or later-stage studies;, our need for substantial additional funds and our ability to raise additional money to fund our operations for at least the next 12 months as a going concern; our ability to successfully commercialize LYMPHIR and establish a sustainable revenue stream; the estimated markets for LYMPHIR and our product candidates and the acceptance thereof by any market; our ability to secure strategic partnerships and expand international access to LYMPHIR; our ability to maintain Nasdaq’s continued listing standards; our ability to use the latest technology to support our commercialization efforts for LYMPHIR; physician and patient acceptance of LYMPHIR in a competitive treatment landscape; our reliance on third-party logistics providers, distributors, and specialty pharmacies to support commercial operations; our ability to educate providers and payers, secure adequate reimbursement, and maintain uninterrupted product supply; post-marketing requirements and ongoing regulatory compliance related to LYMPHIR; the ability of LYMPHIR and our product candidates to impact the quality of life of our target patient populations; our ability to procure cGMP commercial-scale supply; our ability to obtain, perform under and maintain financing and strategic agreements and relationships; market and other conditions; risks related to our growth strategy; patent and intellectual property matters; government regulation; as well as other risks described in our Securities and Exchange Commission (“SEC”) filings. These risks have been and may be further impacted by any future public health risks. Accordingly, these forward-looking statements do not constitute guarantees of future performance, and you are cautioned not to place undue reliance on these forward-looking statements. Risks regarding our business are described in detail in our SEC filings which are available on the SEC’s website at www.sec.gov, including in Citius Oncology’s Annual Report on Form 10-K for the year ended September 30, 2025, filed with the SEC on December 23, 2025. These forward-looking statements speak only as of the date hereof, and we expressly disclaim any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations or any changes in events, conditions or circumstances on which any such statement is based, except as required by law.

REFERENCES:

Tandem Meetings: Transplantation & Cellular Therapy Meetings of the American Society for Transplantation and Cellular Therapy (ASTCT^®) & the Center for International Blood and Marrow Transplant Research (CIBMTR^®)

Yescarta® is a registered trademark of Kite Pharma, Inc., a Gilead company.

Breyanzi® is a registered trademark of Bristol Myers Squibb.

Kymriah® is a registered trademark of Novartis.

LYMPHIR™ (denileukin diftitox-cxdl)

INDICATION

LYMPHIR is an IL2-receptor-directed cytotoxin indicated for the treatment of adult patients with r/r Stage I-III cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy.

IMPORTANT SAFETY INFORMATION

BOXED WARNING: CAPILLARY LEAK SYNDROME

Capillary leak syndrome (CLS), including life-threatening or fatal reactions, can occur in patients receiving LYMPHIR. Monitor patients for signs and symptoms of CLS during treatment. Withhold LYMPHIR until CLS resolves, or permanently discontinue based on severity.

WARNINGS AND PRECAUTIONS

Capillary Leak Syndrome

LYMPHIR can cause capillary leak syndrome (CLS), including life-threatening or fatal reactions. CLS was defined in the clinical trials as the occurrence of at least 2 of the following symptoms at any time during LYMPHIR therapy: hypotension, edema, and serum albumin <3 g/dL. These symptoms were not required to occur simultaneously to be characterized as capillary leak syndrome.

As defined, CLS occurred in 27% of patients in the pooled population across 3 clinical trials, including 8% with Grade 3. There was one (0.8%) fatal occurrence of CLS. Of the patients with CLS, 22% had recurrence. The majority of CLS events (81%) occurred within the first 2 cycles of treatment. The median time to onset from Cycle 1, Day 1 was 6.5 days (range: 1 to 77), the median duration of CLS was 14 days (range: 2 to 40), and 75% of patients had resolution. The most common symptoms included edema, hypoalbuminemia, and hypotension. Pleural effusion, pericardial effusion, and dehydration also occurred.

Regularly assess patients for weight gain, new onset or worsening of edema, dyspnea, and hypotension (including orthostatic changes). Monitor serum albumin levels prior to the initiation of each cycle of therapy and more often as clinically indicated.

Withhold, reduce dose, or permanently discontinue based on severity. If LYMPHIR is withheld, resume LYMPHIR following resolution of CLS and when serum albumin is greater than or equal to 3 g/dL.

Visual Impairment

LYMPHIR can cause serious visual impairment, including changes in visual acuity and color vision. In the pooled population across 3 clinical trials, visual impairment occurred in 9%, with Grade 1 in 8% and Grade 2 in 1%. The most commonly reported symptom was blurred vision. Of the patients with visual impairment, 67% had resolution of their visual impairment.

Perform baseline ophthalmic examination and monitor as clinically indicated. If patients experience symptoms of visual impairment, such as changes in visual acuity, changes in color vision, or blurred vision, refer for ophthalmologic evaluation.

Withhold LYMPHIR until visual impairment resolves or permanently discontinue based on severity.

Infusion-Related Reactions

LYMPHIR can cause serious infusion-related reactions. Infusion-related reactions were reported in 69% of patients in the pooled population across 3 clinical trials of patients who received LYMPHIR, with Grade 3 infusion-related reactions in 3.4%. Eighty-three percent of infusion-related reactions occurred in Cycles 1 and 2. The most common symptoms included nausea, fatigue, chills, musculoskeletal pain, vomiting, fever, and arthralgia.

Premedicate patients for the first three cycles prior to starting a LYMPHIR infusion. Monitor patients frequently during infusion. For Grade 2 or higher infusion reactions, premedicate at least 30 minutes prior to each subsequent infusion with a systemic steroid for at least 3 cycles.

Interrupt or discontinue LYMPHIR based on severity. Institute appropriate medical management.

Hepatotoxicity

LYMPHIR can cause hepatotoxicity. In the pooled safety population, elevated ALT occurred in 70% of patients, with Grade 3 ALT occurring in 22%; elevated AST occurred in 64% of patients, with Grade 3 AST elevation occurring in 9%. For Grade 3 events, median time to onset was 8 days (range: 1 to 15 days); median time to resolution was 15 days (range: 7 to 50 days); all cases of Grade 3 ALT or AST elevations resolved. Elevated total bilirubin occurred in 5% of patients, with Grade 3 occurring in 0.9%.

Monitor liver enzymes and bilirubin at baseline and during treatment as clinically indicated. Withhold, reduce dose, or permanently discontinue LYMPHIR based on severity.

Embryo-Fetal Toxicity

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman. Verify the pregnancy status of females of reproductive potential prior to the initiation of LYMPHIR. Advise pregnant women of the potential risk to the fetus. Advise females of reproductive potential to use effective contraception during treatment and for 7 days following the last dose of LYMPHIR.

ADVERSE REACTIONS

The most common adverse reactions (≥20%), including laboratory abnormalities, are increased transaminases, albumin decreased, nausea, edema, hemoglobin decreased, fatigue, musculoskeletal pain, rash, chills, constipation, pyrexia, and capillary leak syndrome.

USE IN SPECIFIC POPULATIONS

Pregnancy

Risk Summary

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman. There are no available data on the use of LYMPHIR in pregnant women to evaluate for a drug-associated risk. No animal reproductive and developmental toxicity studies have been conducted with denileukin diftitox.

Denileukin diftitox-cxdl causes depletion of regulatory T lymphocytes (Treg), immune activation, and capillary leak syndrome, compromising pregnancy maintenance. Advise pregnant women of the potential risk to a fetus.

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies are 2-4% and 15-20%, respectively.

Lactation

Risk Summary

No data are available regarding the presence of denileukin diftitox-cxdl in human milk, the effects on the breastfed child, or on milk production. Because of the potential for serious adverse reactions in breastfed children, advise women not to breastfeed during treatment with LYMPHIR and for 7 days after the last dose.

Females and Males of Reproductive Potential

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman.

Pregnancy Testing

Verify the pregnancy status of females of reproductive potential prior to initiating LYMPHIR.

Contraception

Females

Advise females of reproductive potential to use effective contraception during treatment with LYMPHIR and for 7 days after the last dose.

Infertility

Males

Based on findings in rats, male fertility may be compromised by treatment with LYMPHIR. The reversibility of the effect on fertility is unknown.

Pediatric Use

Safety and effectiveness of LYMPHIR in pediatric patients have not been established.

Geriatric Use

Of the 69 patients with Stage I-III r/r CTCL who received LYMPHIR, 34 patients (49%) were 65 years of age and older and 10 patients (14%) were 75 years of age and older. Clinical studies of LYMPHIR did not include sufficient numbers of patients 65 years of age and older to determine whether they respond differently from younger adult patients.

You may report side effects to the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. You may also report side effects to Citius Oncology at 1-844-459-6744.

Please read Important Safety Information and full Prescribing Information, including Boxed WARNING, for LYMPHIR.

Investor Contact:

Ilanit Allen

ir@citiuspharma.com

908-967-6677 x113

Media Contact:

STiR-communications

Greg Salsburg

Greg@STiR-communications.com

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) March 10, 2026

Citius Oncology, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

001-41534		99-4362660
(Commission File Number)		(IRS Employer Identification No.)

11 Commerce Drive, 1st Floor, Cranford, NJ		07016
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (908) 967-6677

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock		CTOR		The Nasdaq Capital Market

Emerging growth company ☒

Item 8.01 Other Events.

On March 10, 2026, we issued a press release announcing positive topline results from a completed investigator-initiated Phase 1 clinical trial conducted by University of Pittsburgh investigators. This study evaluated the direct T-regulatory (Treg) cell depletion activity of LYMPHIR™ (denileukin diftitox-cxdl) in combination with the PD-1 immune checkpoint inhibitor pembrolizumab (KEYTRUDA^®) in patients with recurrent or refractory gynecologic cancers, including ovarian and endometrial malignancies. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press release, dated March 10, 2026.
104		Cover Page Interactive Data File, formatted in Inline Extensible Business Reporting Language (iXBRL).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	CITIUS ONCOLOGY, INC.

Date: March 10, 2026	/s/ Leonard Mazur
	Leonard Mazur
	Chairman and Chief Executive Officer

Exhibit 99.1

Citius Oncology Announces Positive Topline Results from Investigator-Initiated Phase 1 Study of LYMPHIR™ in Combination with Pembrolizumab in Relapsed or Refractory Gynecologic Cancers

Study data from patients with relapsed or refractory gynecologic cancers signals the potential of LYMPHIR to augment immune checkpoint inhibitor efficacy

Topline data of University of Pittsburgh-led trial to be presented at an upcoming international cancer conference later this year

CRANFORD, N.J., March 10, 2026 – Citius Oncology, Inc. (“Citius Oncology”) (Nasdaq: CTOR), an oncology-focused biopharmaceutical company and majority-owned subsidiary of Citius Pharmaceuticals, Inc. (“Citius Pharma”) (Nasdaq: CTXR), today announced positive topline results from a completed investigator-initiated Phase 1 clinical trial conducted by University of Pittsburgh investigators. This study evaluated the direct T-regulatory (Treg) cell depletion activity of LYMPHIR™ (denileukin diftitox-cxdl) in combination with the PD-1 immune checkpoint inhibitor pembrolizumab (KEYTRUDA^®) in patients with recurrent or refractory gynecologic cancers, including ovarian and endometrial malignancies.

Patients with relapsed or refractory gynecological cancer have poor prognoses and very limited treatment options. This dose-escalation Phase 1 non-chemotherapy based clinical study aimed to establish a recommended dose of LYMPHIR in combination with pembrolizumab for a Phase 2 study. In 25 evaluable patients, no unexpected safety signals or serious immune-related adverse events were observed at any dose level.

“We are encouraged by the favorable safety profile and sustained disease control observed in this heavily pretreated patient population. Evidence from the study suggests augmented anti-tumor activity when LYMPHIR is combined with KEYTRUDA and warrants further exploration in Phase 2 settings,” stated Dr. Myron Czuczman, Executive Vice President and Chief Medical Officer of Citius Oncology and Citius Pharma.

The trial explored efficacy and demonstrated a 24 % objective response rate (ORR) and a 48 % clinical benefit rate (CBR, defined as complete response, partial response and/or stable disease for six months or greater) among 21 evaluable patients. Full safety and clinical efficacy results are expected to be presented at an international cancer conference later this year.

“The efficacy signal shown by this combination is incredibly exciting considering the minimal impact immuno-oncology has made in ovarian cancer thus far. If these findings are confirmed in subsequent studies, we may have a transformational therapy on our hands,” said Dr. Alexander Olawaiye, principal investigator of the study.

About the Study

This open-label, dose-escalation, investigator-initiated Phase 1 study (NCT05200559), led by Dr. Alexander B Olawaiye at UPMC Magee-Women’s Hospital, enrolled patients with recurrent or metastatic solid tumors who had received at least one prior line of therapy. LYMPHIR was administered intravenously on Days 1–3 of each 21-day cycle at escalating doses (3, 6, 9, and 12 mcg/kg), along with pembrolizumab (200 mg IV) on Day 1. Patients who completed eight cycles of combination therapy were continued on pembrolizumab monotherapy until disease progression.

About Gynecologic Cancers

Recurrent or metastatic ovarian and endometrial cancers are two of the most common gynecologic malignancies in the United States. Endometrial cancer is the most frequently diagnosed gynecologic cancer, with an estimated 70,000 new cases expected in 2026¹, while ovarian cancer remains the deadliest with approximately 12,700 deaths per year (51.6% 5 year survival) and approximately 20,000 new diagnoses each year². These cancers are often detected at advanced stages, and although many patients initially respond to platinum-based chemotherapy, most experience relapse and develop resistance. Survival rates in the recurrent setting remain poor, and responses to current immunotherapies such as PD-1 inhibitors are limited, highlighting a significant unmet need for novel treatment approaches. LYMPHIR’s transient depletion of regulatory T-cells may enhance anti-tumor immune responses and help overcome immunotherapy resistance in these difficult-to-treat tumors.

About LYMPHIR™ (denileukin diftitox-cxdl)

About Citius Oncology, Inc.

Forward-Looking Statements

This press release may contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such statements are made based on our expectations and beliefs concerning future events impacting Citius Oncology. You can identify these statements by the fact that they use words such as “will,” “anticipate,” “estimate,” “expect,” “plan,” “should,” and “may” and other words and terms of similar meaning or use of future dates. Forward-looking statements are based on management’s current expectations and are subject to risks and uncertainties that could negatively affect our business, operating results, financial condition and stock price. Factors that could cause actual results to differ materially from those currently anticipated are: risks relating to the results of research and development activities, including those from our existing and any new pipeline assets; early-stage clinical data may not be predictive of results from larger or later-stage studies; our need for substantial additional funds and our ability to raise additional money to fund our operations for at least the next 12 months as a going concern; our ability to successfully commercialize LYMPHIR and establish a sustainable revenue stream; the estimated markets for LYMPHIR and our product candidates and the acceptance thereof by any market; our ability to secure strategic partnerships and expand international access to LYMPHIR; our ability to maintain Nasdaq’s continued listing standards; our ability to use the latest technology to support our commercialization efforts for LYMPHIR; physician and patient acceptance of LYMPHIR in a competitive treatment landscape; our reliance on third-party logistics providers, distributors, and specialty pharmacies to support commercial operations; our ability to educate providers and payers, secure adequate reimbursement, and maintain uninterrupted product supply; post-marketing requirements and ongoing regulatory compliance related to LYMPHIR; the ability of LYMPHIR and our product candidates to impact the quality of life of our target patient populations; our ability to procure cGMP commercial-scale supply; our ability to obtain, perform under and maintain financing and strategic agreements and relationships; market and other conditions; risks related to our growth strategy; patent and intellectual property matters; government regulation; as well as other risks described in our Securities and Exchange Commission (“SEC”) filings. These risks have been and may be further impacted by any future public health risks. Accordingly, these forward-looking statements do not constitute guarantees of future performance, and you are cautioned not to place undue reliance on these forward-looking statements. Risks regarding our business are described in detail in our SEC filings which are available on the SEC’s website at www.sec.gov, including in Citius Oncology’s Annual Report on Form 10-K for the year ended September 30, 2025, filed with the SEC on December 23, 2025. These forward-looking statements speak only as of the date hereof, and we expressly disclaim any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations or any changes in events, conditions or circumstances on which any such statement is based, except as required by law.

REFERENCES:

1.	American Cancer Society. Cancer Facts & Figures 2026 (projected). Atlanta: American Cancer Society; 2026. https://www.cancer.org/cancer/types/endometrial-cancer/about/key-statistics.html

2.	National Cancer Institute. Surveillance, Epidemiology, and End Results Program (SEER). Cancer Stat Facts: Uterine and Ovarian Cancer. https://seer.cancer.gov/statfacts/html/ovary.html

KEYTRUDA^® is a registered trademark of Merck & Co., Inc.

LYMPHIR™ (denileukin diftitox-cxdl)

INDICATION

LYMPHIR is an IL2-receptor-directed cytotoxin indicated for the treatment of adult patients with r/r Stage I-III cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy.

IMPORTANT SAFETY INFORMATION

BOXED WARNING: CAPILLARY LEAK SYNDROME

WARNINGS AND PRECAUTIONS

Capillary Leak Syndrome

Withhold, reduce dose, or permanently discontinue based on severity. If LYMPHIR is withheld, resume LYMPHIR following resolution of CLS and when serum albumin is greater than or equal to 3 g/dL.

Visual Impairment

Withhold LYMPHIR until visual impairment resolves or permanently discontinue based on severity.

Infusion-Related Reactions

Interrupt or discontinue LYMPHIR based on severity. Institute appropriate medical management.

Hepatotoxicity

Monitor liver enzymes and bilirubin at baseline and during treatment as clinically indicated. Withhold, reduce dose, or permanently discontinue LYMPHIR based on severity.

Embryo-Fetal Toxicity

ADVERSE REACTIONS

USE IN SPECIFIC POPULATIONS

Pregnancy

Risk Summary

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies are 2-4% and 15-20%, respectively.

Lactation

Risk Summary

Females and Males of Reproductive Potential

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman.

Pregnancy Testing

Verify the pregnancy status of females of reproductive potential prior to initiating LYMPHIR.

Contraception

Females

Advise females of reproductive potential to use effective contraception during treatment with LYMPHIR and for 7 days after the last dose.

Infertility

Males

Based on findings in rats, male fertility may be compromised by treatment with LYMPHIR. The reversibility of the effect on fertility is unknown.

Pediatric Use

Safety and effectiveness of LYMPHIR in pediatric patients have not been established.

Geriatric Use

You may report side effects to the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. You may also report side effects to Citius Oncology at 1-844-459-6744.

Please read Important Safety Information and full Prescribing Information, including Boxed WARNING, for LYMPHIR.

Investor Contact:

Ilanit Allen

ir@citiuspharma.com

908-967-6677 x113

Media Contact:

STiR-communications

Greg Salsburg

Greg@STiR-communications.com

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) March 31, 2026

Citius Oncology, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

001-41534		99-4362660
(Commission File Number)		(IRS Employer Identification No.)

11 Commerce Drive, 1st Floor, Cranford, NJ		07016
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (908) 967-6677

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock		CTOR		The Nasdaq Capital Market

Emerging growth company ☒

Item 8.01 Other Events.

On March 31, 2026, we issued a press release announcing a commercial update on the U.S. launch of LYMPHIR™ (denileukin diftitox-cxdl). A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press release, dated March 31, 2026.
104		Cover Page Interactive Data File, formatted in Inline Extensible Business Reporting Language (iXBRL).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	CITIUS ONCOLOGY, INC.

Date: March 31, 2026	/s/ Leonard Mazur
	Leonard Mazur
	Chairman and Chief Executive Officer

Exhibit 99.1

Citius Oncology Provides Commercial Update on LYMPHIR™ Launch Highlighting Early
Adoption and Expanding Clinical Development

Broad institutional uptake among leading cancer centers and payer coverage supports early
prescribing momentum and clinical integration

CRANFORD, N.J., March 31, 2026 – Citius Oncology, Inc. (“Citius Oncology”) (Nasdaq: CTOR), an oncology-focused biopharmaceutical company and majority-owned subsidiary of Citius Pharmaceuticals, Inc. (“Citius Pharma”) (Nasdaq: CTXR), today provided a commercial update on the U.S. launch of LYMPHIR™ (denileukin diftitox-cxdl) for the treatment of cutaneous T-cell lymphoma (CTCL), highlighting continued adoption across leading oncology centers, broad payer coverage progress, and advancing investigator-led clinical studies.

“We are encouraged by the early commercial indicators for LYMPHIR, including the pace of formulary adoption, breadth of payer coverage, and increasing repeat orders from leading oncology centers,” said Leonard Mazur, Chairman and CEO of Citius Oncology and Citius Pharma. “As our commercial organization continues to scale and institutions complete formulary inclusion, we expect continued expansion in prescribing activity, including into community settings. Together with further clinical validation through ongoing investigator-led studies, these trends support LYMPHIR’s potential not only for continued integration in the CTCL treatment landscape, but also its potential as a part of a combination immunotherapy regimen in other cancers.”

Key Early Launch Metrics:

●

Sequential growth in orders from target institutions since launch, with initial accounts already placing repeat orders, indicating early prescribing continuity;

●

Strong institutional uptake, with 83% of target accounts having added or actively progressing LYMPHIR through formulary review;

	●	Broad and expanding market access with ~135 health plans, representing ~80% of covered lives, secured and reimbursement systems established;

●

No reported reimbursement denials or prior authorization barriers;

●

Increasing demand for in-services and clinical education;

●

Initial penetration into community infusion centers underway with patients beginning to transition from larger cancer centers; and,

●

Commercial buildout proceeding, with field team onboarding in the coming month and broader field expansion in progress with our contracted sales organization.

Commercial Execution Advancing with Expanding Market Access and Field Deployment

Commercial execution continues to advance with the onboarding of field teams, targeted deployment of medical education and digital campaigns, attendance at major medical meetings and increasing interaction with physicians, pharmacy stakeholders, and community centers to support the finalization of order sets and initiate patient treatment, which typically precedes broader patient start acceleration following formulary inclusion.

Commercial supply remains well positioned to support anticipated U.S. demand, and international expansion is underway through executed distribution agreements across Europe and the Middle East.

Clinical Development Expands Through Leading Academic Collaborations

In parallel, Citius Oncology is advancing LYMPHIR’s clinical development through collaborations with leading academic centers to further evaluate its potential across broader oncology settings. At the University of Minnesota, an investigator-sponsored study is evaluating LYMPHIR prior to CAR-T therapy in relapsed/refractory diffuse large B-cell lymphoma, with positive topline data presented at the ASTCT 2026 Annual Meeting and additional analyses underway. At UPMC, a Phase I study evaluating LYMPHIR in combination with pembrolizumab in solid tumors has been completed, with positive topline results submitted for presentation at an upcoming oncology conference. Discussions are ongoing regarding next-stage development. These efforts support a broader strategy to evaluate LYMPHIR as a potential combination therapy across immuno-oncology settings.

Together, these commercial and clinical developments support a disciplined launch trajectory and provide a solid foundation for continued adoption of LYMPHIR.

About LYMPHIR™ (denileukin diftitox-cxdl)

About Citius Oncology, Inc.

Forward-Looking Statements

This press release may contain “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such statements are made based on our expectations and beliefs concerning future events impacting Citius Oncology. You can identify these statements by the fact that they use words such as “will,” “anticipate,” “estimate,” “expect,” “plan,” “should,” and “may” and other words and terms of similar meaning or use of future dates. Forward-looking statements are based on management’s current expectations and are subject to risks and uncertainties that could negatively affect our business, operating results, financial condition and stock price. Factors that could cause actual results to differ materially from those currently anticipated are: our ability to successfully commercialize LYMPHIR and establish a sustainable revenue stream; risks relating to the results of research and development activities, including those from our existing and any new pipeline assets; our need for substantial additional funds and our ability to raise additional money to fund our operations for at least the next 12 months as a going concern; the estimated markets for LYMPHIR and our product candidates and the acceptance thereof by any market; early-stage clinical data may not be predictive of results from larger or later-stage studies; our ability to maintain Nasdaq’s continued listing standards; our ability to secure strategic partnerships and expand international access to LYMPHIR; our ability to use the latest technology to support our commercialization efforts for LYMPHIR; physician and patient acceptance of LYMPHIR in a competitive treatment landscape; our reliance on third-party logistics providers, distributors, and specialty pharmacies to support commercial operations; our ability to educate providers and payers, secure adequate reimbursement, and maintain uninterrupted product supply; post-marketing requirements and ongoing regulatory compliance related to LYMPHIR; the ability of LYMPHIR and our product candidates to impact the quality of life of our target patient populations; our ability to procure cGMP commercial-scale supply; our ability to obtain, perform under and maintain financing and strategic agreements and relationships; market and other conditions; risks related to our growth strategy; patent and intellectual property matters; government regulation; as well as other risks described in our Securities and Exchange Commission (“SEC”) filings. These risks have been and may be further impacted by any future public health risks. Accordingly, these forward-looking statements do not constitute guarantees of future performance, and you are cautioned not to place undue reliance on these forward-looking statements. Risks regarding our business are described in detail in our SEC filings which are available on the SEC’s website at www.sec.gov, including in Citius Oncology’s Annual Report on Form 10-K for the year ended September 30, 2025, filed with the SEC on December 23, 2025. These forward-looking statements speak only as of the date hereof, and we expressly disclaim any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations or any changes in events, conditions or circumstances on which any such statement is based, except as required by law.

LYMPHIR™ (denileukin diftitox-cxdl)

INDICATION

LYMPHIR is an IL2-receptor-directed cytotoxin indicated for the treatment of adult patients with r/r Stage I-III cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy.

IMPORTANT SAFETY INFORMATION

BOXED WARNING: CAPILLARY LEAK SYNDROME

WARNINGS AND PRECAUTIONS

Capillary Leak Syndrome

Withhold, reduce dose, or permanently discontinue based on severity. If LYMPHIR is withheld, resume LYMPHIR following resolution of CLS and when serum albumin is greater than or equal to 3 g/dL.

Visual Impairment

Withhold LYMPHIR until visual impairment resolves or permanently discontinue based on severity.

Infusion-Related Reactions

Interrupt or discontinue LYMPHIR based on severity. Institute appropriate medical management.

Hepatotoxicity

Monitor liver enzymes and bilirubin at baseline and during treatment as clinically indicated. Withhold, reduce dose, or permanently discontinue LYMPHIR based on severity.

Embryo-Fetal Toxicity

ADVERSE REACTIONS

USE IN SPECIFIC POPULATIONS

Pregnancy

Risk Summary

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies are 2-4% and 15-20%, respectively.

Lactation

Risk Summary

Females and Males of Reproductive Potential

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman.

Pregnancy Testing

Verify the pregnancy status of females of reproductive potential prior to initiating LYMPHIR.

Contraception

Females

Advise females of reproductive potential to use effective contraception during treatment with LYMPHIR and for 7 days after the last dose.

Infertility

Males

Based on findings in rats, male fertility may be compromised by treatment with LYMPHIR. The reversibility of the effect on fertility is unknown.

Pediatric Use

Safety and effectiveness of LYMPHIR in pediatric patients have not been established.

Geriatric Use

You may report side effects to the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. You may also report side effects to Citius Oncology at 1-844-459-6744.

Please read Important Safety Information and full Prescribing Information, including Boxed WARNING, for LYMPHIR.

Investor Contact:

Ilanit Allen

ir@citiuspharma.com

908-967-6677 x113

Media Contact:

STiR-communications

Greg Salsburg

Greg@STiR-communications.com

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) April 22, 2026

Citius Oncology, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

001-41534		99-4362660
(Commission File Number)		(IRS Employer Identification No.)

11 Commerce Drive, 1st Floor, Cranford, NJ		07016
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (908) 967-6677

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock		CTOR		The Nasdaq Capital Market

Emerging growth company ☒

Item 3.01. Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing.

On April 22, 2026, Nasdaq Stock Market LLC (“Nasdaq”) notified Citius Oncology, Inc. (the “Company”) that for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued inclusion on the Nasdaq Capital Market pursuant to Nasdaq Listing Rule 5550(a)(2) (the “Bid Price Rule”).

In accordance with Nasdaq Listing Rule 5810(c)(3)(A), the Company has a compliance period of 180 calendar days, or until October 19, 2026, to regain compliance with the Bid Price Rule. If at any time before October 19, 2026, the bid price of the Company’s common stock closes at $1.00 per share or more for a minimum of ten consecutive business days, Nasdaq will provide the Company with written confirmation of compliance with the Bid Price Rule.

If the Company does not regain compliance with the Bid Price Rule by October 19, 2026, the Company may be eligible for an additional 180-day compliance period. To qualify, the Company would be required to meet the continued listing requirement for market value of publicly held shares and all other initial listing standards for the Nasdaq Capital Market, with the exception of the Bid Price Rule, and would need to provide written notice of its intention to cure the bid price deficiency during the second compliance period by effecting a reverse stock split, if necessary.

If the Company does not regain compliance with the Bid Price Rule when required, Nasdaq will provide written notification to the Company that its common stock is subject to delisting. At that time, the Company may appeal the delisting determination to a Nasdaq hearings panel.

The notice from Nasdaq has no immediate effect on the listing of the Company’s common stock and its common stock will continue to be listed on the Nasdaq Capital Market under the symbol “CTOR”. The Company is currently evaluating its options for regaining compliance. There can be no assurance that the Company will regain compliance with the Bid Price Rule or maintain compliance with any of the other Nasdaq continued listing requirements.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	CITIUS ONCOLOGY, INC.

Date: April 28, 2026	/s/ Leonard Mazur
	Leonard Mazur
	Chairman and Chief Executive Officer

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) April 29, 2026

Citius Oncology, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

001-41534		99-4362660
(Commission File Number)		(IRS Employer Identification No.)

11 Commerce Drive, 1st Floor, Cranford, NJ		07016
(Address of principal executive offices)		(Zip Code)

Registrant’s telephone number, including area code (908) 967-6677

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐

Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐

Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐

Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐

Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock		CTOR		The Nasdaq Capital Market

Emerging growth company ☒

Item 8.01 Other Events.

On April 29, 2026, Citius Oncology, Inc. issued a press release announcing the initial shipment of LYMPHIR™ (denileukin diftitox-cxdl) to Europe through one of its regional distribution partners. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) Exhibits

Exhibit No.		Description
99.1		Press release, dated April 29, 2026.
104		Cover Page Interactive Data File, formatted in Inline Extensible Business Reporting Language (iXBRL).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	CITIUS ONCOLOGY, INC.

Date: April 29, 2026	/s/ Leonard Mazur
	Leonard Mazur
	Chairman and Chief Executive Officer

Exhibit 99.1

Citius Oncology Ships First International Order of LYMPHIR™ to Europe

Order fulfilment expands international patient access to LYMPHIR following initial U.S. launch

Distribution by regional partners through Named Patient Programs in specific international markets

CRANFORD, N.J., April 29, 2026 – Citius Oncology, Inc. (“Citius Oncology”) (Nasdaq: CTOR), an oncology-focused biopharmaceutical company and majority-owned subsidiary of Citius Pharmaceuticals, Inc. (“Citius Pharma”) (Nasdaq: CTXR), today announced the initial shipment of LYMPHIR™ (denileukin diftitox-cxdl) to Europe through one of its regional distribution partners, marking an important milestone in expanding access to the therapy for patients outside the United States. LYMPHIR will be made available to eligible patients through Named Patient Programs (NPPs) in accordance with local regulations in each country.

The initiation of European distribution represents a strategic step in the Company’s broader effort to extend access to LYMPHIR for patients with limited treatment options, while continuing to prioritize disciplined and targeted market entry.

“Reaching this milestone underscores our commitment to ensuring that patients in need can access LYMPHIR beyond the United States,” said Leonard Mazur, Chairman and Chief Executive Officer of Citius Oncology. “Through our distribution partners, we are enabling physicians to request LYMPHIR for appropriate patients via established Named Patient Programs, providing a pathway to treatment where approved alternatives may be limited. Importantly, this progress complements the strong early foundation we are building in the U.S., where we continue to see encouraging adoption across key treatment centers.”

In the United States, Citius Oncology continues to execute its commercial launch strategy, with ongoing progress in formulary access, expanding payer coverage, and increasing engagement across both academic and community oncology settings. The Company remains focused on supporting physician education and facilitating patient access as LYMPHIR becomes integrated into clinical practice.

LYMPHIR was approved by the U.S. Food and Drug Administration in August 2024 for the treatment of adult patients with Stage I–III relapsed or refractory cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy, and was commercially launched in the United States in December 2025.

LYMPHIR does not have marketing authorization from the European Medicines Agency in Europe or other countries outside the United States. Access is being provided solely through Named Patient Programs in accordance with applicable local laws and regulations.

About LYMPHIR™ (denileukin diftitox-cxdl)

About Citius Oncology, Inc.

Forward-Looking Statements

This press release may contain "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Such statements are made based on our expectations and beliefs concerning future events impacting Citius Oncology. You can identify these statements by the fact that they use words such as "will," "anticipate," "estimate," "expect," "plan," "should," and "may" and other words and terms of similar meaning or use of future dates. Forward-looking statements are based on management's current expectations and are subject to risks and uncertainties that could negatively affect our business, operating results, financial condition and stock price. Factors that could cause actual results to differ materially from those currently anticipated are: our ability to successfully commercialize LYMPHIR and establish a sustainable revenue stream; our ability to secure and maintain strategic partnerships and expand international access to LYMPHIR; the estimated markets for LYMPHIR and our product candidates and the acceptance thereof by any market; risks relating to the results of research and development activities, including those from our existing and any new pipeline assets; our need for substantial additional funds and our ability to raise additional money to fund our operations for at least the next 12 months as a going concern; early-stage clinical data may not be predictive of results from larger or later-stage studies; our ability to maintain Nasdaq’s continued listing standards; our ability to use the latest technology to support our commercialization efforts for LYMPHIR; physician and patient acceptance of LYMPHIR in a competitive treatment landscape; our reliance on third-party logistics providers, distributors, and specialty pharmacies to support commercial operations; our ability to educate providers and payers, secure adequate reimbursement, and maintain uninterrupted product supply; post-marketing requirements and ongoing regulatory compliance related to LYMPHIR; the ability of LYMPHIR and our product candidates to impact the quality of life of our target patient populations; our ability to procure cGMP commercial-scale supply; our ability to obtain, perform under and maintain financing and strategic agreements and relationships; market and other conditions; risks related to our growth strategy; patent and intellectual property matters; government regulation; as well as other risks described in our Securities and Exchange Commission (“SEC”) filings. These risks have been and may be further impacted by any future public health risks. Accordingly, these forward-looking statements do not constitute guarantees of future performance, and you are cautioned not to place undue reliance on these forward-looking statements. Risks regarding our business are described in detail in our SEC filings which are available on the SEC’s website at www.sec.gov, including in Citius Oncology’s Annual Report on Form 10-K for the year ended September 30, 2025, filed with the SEC on December 23, 2025. These forward-looking statements speak only as of the date hereof, and we expressly disclaim any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations or any changes in events, conditions or circumstances on which any such statement is based, except as required by law.

LYMPHIR™ (denileukin diftitox-cxdl)

INDICATION

LYMPHIR is an IL2-receptor-directed cytotoxin indicated for the treatment of adult patients with r/r Stage I-III cutaneous T-cell lymphoma (CTCL) after at least one prior systemic therapy.

IMPORTANT SAFETY INFORMATION

BOXED WARNING: CAPILLARY LEAK SYNDROME

WARNINGS AND PRECAUTIONS

Capillary Leak Syndrome

Withhold, reduce dose, or permanently discontinue based on severity. If LYMPHIR is withheld, resume LYMPHIR following resolution of CLS and when serum albumin is greater than or equal to 3 g/dL.

Visual Impairment

Withhold LYMPHIR until visual impairment resolves or permanently discontinue based on severity.

Infusion-Related Reactions

Interrupt or discontinue LYMPHIR based on severity. Institute appropriate medical management.

Hepatotoxicity

Monitor liver enzymes and bilirubin at baseline and during treatment as clinically indicated. Withhold, reduce dose, or permanently discontinue LYMPHIR based on severity.

Embryo-Fetal Toxicity

ADVERSE REACTIONS

USE IN SPECIFIC POPULATIONS

Pregnancy

Risk Summary

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies are 2-4% and 15-20%, respectively.

Lactation

Risk Summary

Females and Males of Reproductive Potential

Based on its mechanism of action, LYMPHIR can cause fetal harm when administered to a pregnant woman.

Pregnancy Testing

Verify the pregnancy status of females of reproductive potential prior to initiating LYMPHIR.

Contraception

Females

Advise females of reproductive potential to use effective contraception during treatment with LYMPHIR and for 7 days after the last dose.

Infertility

Males

Based on findings in rats, male fertility may be compromised by treatment with LYMPHIR. The reversibility of the effect on fertility is unknown.

Pediatric Use

Safety and effectiveness of LYMPHIR in pediatric patients have not been established.

Geriatric Use

You may report side effects to the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. You may also report side effects to Citius Oncology at 1-844-459-6744.

Please read Important Safety Information and full Prescribing Information, including Boxed WARNING, for LYMPHIR.

Investor Contact:

Ilanit Allen

ir@citiuspharma.com

908-967-6677 x113

Media Contact:

STiR-communications

Greg Salsburg

Greg@STiR-communications.com

SEC Form 424B3 filed by Citius Oncology Inc.