Summit Therapeutics Inc美股招股说明书(2025-08-11版)

Common stock We have previously entered into a distribution agreement dated May13, 2024 (the “Original Distribution Agreement”) with J.P. Morgan Securities LLC(which we refer to as the “Sales Agent”), relating to shares of our common stock, par value $0.01 per share, offered by this prospectus supplement andaccompanying prospectus. As of May13, 2024, shares of common stock with an aggregate offering price of up to $90,000,000 were available for salepursuant to the Original Distribution Agreement. As of August8, 2025, 1,807,093 shares of common stock, with an aggregate offering price ofapproximately $44.2million, were sold under the Original Distribution Agreement pursuant to a prospectus supplement dated May13, 2024 (the “InitialProspectus Supplement”). On August11, 2025, we entered into an amendment to the Original Distribution Agreement (as amended, the DistributionAgreement”), which increased the aggregate offering price of common shares we may offer and sell from time to time through the Sales Agent under theDistribution Agreement by an additional $360,000,000 as of the date of this prospectus supplement. We do not expect to make any sales under thisprospectus supplement unless and until we sell the remaining available shares issuable under the Initial Prospectus Supplement. Sales of the shares ofcommon stock, if any, may be made on The Nasdaq Global Market at market prices and such other sales as agreed upon by us and the Sales Agent, asthe case may be. Our common stock is listed on The Nasdaq Global Market under the symbol “SMMT.” On August8, 2025, the closing price of our common stock, asreported on The Nasdaq Global Market, was $28.66 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 their 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-20 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-12 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 August11, 2025 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 prospectusCautionary note regarding forward-looking statementsRisk factorsUse of proceeds Table of Contents About this prospectus supplement This prospectus supplement and the accompanying prospectus are part of a registration statement on FormS-3that we filed with the Securities andExchange Commission (the “SEC”) using a “shelf” registration process. The $360,000,000 of common stock that may be offered, issued and sold underthis prospectus supplement is included in the $450,000,000 of securities that may be offered, issued and sold by us pursuant to the registration statement. This prospectus supplement relates to an offering of our common stock. Before buying any of the common stock that we are offering, we urge you tocarefully read this prospectus supplement and the accompanying prospectus, together with