Summit Therapeutics Inc美股招股说明书(2026-06-10版)

Preliminary prospectus supplement(To the prospectus dated June9, 2026) $500,000,000 Common stock Our common stock is listed on The Nasdaq Global Market under the symbol “SMMT.” The last reported sale price of ourcommon stock on The Nasdaq Global Market on June8, 2026 was $14.11 per share. At an assumed public offering price of$14.11 per share, we would offer 35,435,861 shares of our common stock in this offering. PershareTotalPublic offering price$$Underwriting discounts and commissions(1)$$Proceed to Summit Therapeutics Inc., before expenses$$ (1)See “Underwriting” for additional information regarding underwriting compensation. We have granted the underwriters an option for a period of 30 days from the date of this prospectus supplement to purchase upto $75,000,000 of additional shares of our common stock from us at the public offering price less the underwriting discounts andcommissions. Investing in our common stock involves significant risks. See “Risk factors” on page S-6 of this prospectus supplementand in the documents incorporated by reference in this prospectus supplement concerning factors you should considerbefore investing in our securities. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved ofthese securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus.Any representation to the contrary is a criminal offense. The underwriters expect to deliver the shares of common stock to purchasers on or about June, 2026. J.P.Morgan Citigroup The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and theaccompanying prospectus are not an offer to sell these securities and we are not soliciting an offer to buy these securities in any jurisdiction where theoffer or sale is not permitted.June, 2026 Table of Contents Table of contents ABOUT THIS PROSPECTUS SUPPLEMENTPROSPECTUS SUPPLEMENT SUMMARYTHE OFFERINGRISK FACTORSSPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTSUSE OF PROCEEDSDILUTIONMATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES TO NON-U.S. HOLDERSUNDERWRITINGLEGAL MATTERSEXPERTSWHERE YOU CAN FIND MORE INFORMATION; INCORPORATION BY REFERENCE Prospectus ABOUT THIS PROSPECTUS CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTSPROSPECTUS SUMMARYRISK FACTORSUSE OF PROCEEDSDESCRIPTION OF CAPITAL STOCK Table of Contents About this prospectus supplement This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stock and alsoadds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectussupplement and the accompanying prospectus. The second part is the accompanying prospectus dated June9, 2026, included in our registrationstatement on Form S-3 (File No.333-296642), along with the documents incorporated by reference therein, which provides more general information,some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. Tothe extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in theaccompanying prospectus or in any document incorporated by reference that was filed with the Securities and Exchange Commission (the “SEC”)before the date of this prospectus supplement, on the other hand, you should rely on the information contained in this prospectus supplement. If anystatement in one of these documents is inconsistent with a statement in another document having a later date-for example, a document incorporated byreference in the accompanying prospectus-the statement in the document having the later date modifies or supersedes the earlier statement. This prospectus supplement and the accompanying prospectus are part of a “shelf” registration statement that we filed with the SEC. Under this shelfregistration process, we may offer from time to time various securities, of which this offering of shares of our common stock is a part. Such registrationstatement also includes exhibits that provide more detail on the matters discussed in this prospectus supplement and the accompanying prospectus. Youshould read this prospectus supplement, the accompanying prospectus, including the information incorporated by reference herein and therein, theexhibits filed with the SEC, and any free writing prospectus that we have authorized for use in connection with this offering, in their entirety beforemaking an investment decision. We have not, and the underwriters have not, authorized anyone to provide you with information, or to make any representation, different from thatcontained or incorporated by reference in this prospectus supplement and the accompanying prospectus, along with the informatio