Summit Therapeutics Inc美股招股说明书(2026-07-23版)

Up to $380,000,000 Common stock We have entered into a distribution agreement dated July23, 2026 (the “Distribution Agreement”) with J.P.Morgan Securities LLC (which we refer toas the “Sales Agent”), relating to shares of our common stock, par value $0.01 per share, offered by this prospectus supplement and accompanyingprospectus. In accordance with the terms of the Distribution Agreement, we may offer and sell shares of our common stock having an aggregate offeringprice of up to $380,000,000 from time to time through the Sales Agent. Sales of the shares of common stock, if any, may be made on The Nasdaq GlobalMarket at market prices and such other sales as agreed upon by us and the Sales Agent, as the case may be. Our common stock is listed on The Nasdaq Global Market under the symbol “SMMT.” On July22, 2026, the closing price of our common stock, asreported on The Nasdaq Global Market, was $14.74 per share. Sales of our common stock, if any, under this prospectus supplement will be made in sales deemed to be an “at the market offering” as defined in Rule415(a)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”). The Sales Agent is not required to sell any specific numberor dollar amount of securities, but will use commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be soldby us, consistent with its normal trading and sales practices, on mutually agreed terms between the Sales Agent and us. There is no arrangement forfunds to be received in any escrow, trust or similar arrangement. The Sales Agent will be entitled to compensation at a commission rate of up to 3.0% of the gross sales price of common stock sold under theDistribution Agreement. In connection with the sale of the common stock on our behalf, the Sales Agent may be deemed to be an “underwriter” withinthe meaning of the Securities Act and the compensation of the Sales Agent may be deemed to be underwriting commissions or discounts. We have alsoagreed to provide indemnification and contribution to the Sales Agent with respect to certain liabilities, including liabilities under the Securities Act orthe Securities Exchange Act of 1934, as amended (the “Exchange Act”). See “Plan of Distribution” beginning on page S-15 for additional informationregarding the compensation to be paid to the Sales Agent. Investing in our common stock involves a high degree of risk. You should review carefully the risks and uncertaintiesreferenced under the heading “Risk Factors” on page S-7 of this prospectus supplement and in the documentsincorporated by reference into this prospectus supplement. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, ordetermined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is acriminal offense. J.P. Morgan The date of this prospectus supplement is July23, 2026 Table of Contents Table of contents Prospectus supplement About this prospectus supplementProspectus supplement summaryThe offeringRisk factorsCautionary statement regarding forward-looking statementsUse of proceedsDividend policyDilutionPlan of distributionLegal mattersExpertsWhere you can find more informationIncorporation of certain information by reference Prospectus About this prospectus Cautionary note regarding forward-looking statementsProspectus summaryRisk factorsUse of proceedsDescription of capital stockDescription of debt securitiesDescription of depositary sharesDescription of warrantsDescription of subscription rightsDescription of unitsDividend policySelling securityholdersPlan of distributionLegal mattersExpertsWhere you can find more informationIncorporation of certain information by reference 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, which provides more general information.Thisprospectus supplement and the accompanying prospectus are part of an automatic registration statement on FormS-3 that we filed with the Securitiesand Exchange Commission (the “SEC”) utilizing the SEC’s “shelf” registration process.Generally, when we refer to this prospectus supplement, we arereferring to both parts of this document combined. To the extent the information contained in this prospectus supplement differs from or conflicts withthe information contained in the accompanying prospectus or any document incorporated by reference, the information in this prospectus supplementwill control. If any statement in one of these documents is inconsistent with