Citius Oncology Inc美股招股说明书(2026-05-06版)

This prospectus supplement updates, amends and supplements the prospectus dated March 2, 2026 (as supplemented oramended from time to time, the “Prospectus”), which forms a part of the Post-Effective Amendment to the Registration Statement onForm S-1 (Registration No. 333-288656). Capitalized terms used in this prospectus supplement and not otherwise defined herein havethe meanings specified in the Prospectus. This prospectus supplement is being filed to update, amend and supplement the information included in the Prospectus withthe information contained in our Current Report on Form8-K filed with the Securities and Exchange Commission on May 6, 2026 (the “Current Report”). Accordingly, we have attached the Current Report 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 orutilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplementshould be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and thisprospectus 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 ourCommon Stock on May 5, 2026, was $0.9569 per share. Investing in our securities involves a high degree of risk, including the risk of losing your entire investment. See “RiskFactors” 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 thesesecurities or passed upon the accuracy or adequacy of this prospectus supplement. Any representation to the contrary is acriminal offense. The date of this prospectus supplement is May 6, 2026 UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549 FORM 8-K CURRENT REPORTPursuant to Section 13 or 15(d) ofthe Securities Exchange Act of 1934 Date of Report (Date of earliest event reported)May 4, 2026 Citius Oncology, Inc.(Exact name of registrant as specified in its charter) Delaware(State or other jurisdiction of incorporation) 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 registrantunder 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: 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 forcomplying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.☐ Item 1.01 Entry into a Material Definitive Agreement. Warrant Inducement Transaction On May 5, 2026, Citius Oncology, Inc. (the “Company”), entered into a warrant inducement agreement (the “WarrantInducement Agreement”) with the holder of certain existing warrants to purchase up to an aggregate of 12,777,778 shares of theCompany’s common stock, which consists of all of the 6,818,182 shares underlying warrants originally issued on July 16, 2025, all ofthe 5,142,858 shares underlying warrants originally issued on September 10, 2025, and 816,738 shares underlying warrants originallyissued December 10, 2025, each with an exercise price of $1.09 per share (together, the “Induced Warrants”). As an inducement to theholder for exercising the Induced Warrants in cash at a reduced exercise price of $0.90 per share, the Company’s issued to the holdernew warrants to purchase up to an aggregate of 25,555,556 shares of the Company’s common stock, which have similar terms to theInduced Warrants, other than an exercise price of $0.90 and the terms discussed below (the “New Warrants”). The shares of common stock underlying the Induced Warrants originally issued on July 16, 2025 are registered on theRegistration Statement on Form S-1 (Registration Statement No. 333-282792) for which Post-Effective Amendment No. 1 was filedwith the SEC on February 20, 2026 and declared effective by the Securities Exchange Commission (the “SEC”) on March 2, 2026.T