Summit Therapeutics Inc. (Nasdaq: SMMT) (“Summit,” “we,” or the “Company”) today announced that it has commenced an underwritten public offering of $500.0 million of shares of its common stock. All of the shares in the proposed offering are being offered by Summit. In addition, Summit intends to grant the underwriters a 30-day option to purchase up to an additional $75.0 million of shares of its common stock at the public offering price, less underwriting discounts and commissions. The proposed offering is subject to market and other conditions, and there can be no assurance as to whether or when the offering may be completed, or as to the actual size or terms of the offering.

Summit intends to use the net proceeds from the proposed offering, together with its existing cash, cash equivalents, to fund the research and development of its lead product candidate, ivonescimab, and for working capital and other general corporate purposes.

J.P. Morgan, Goldman Sachs & Co. LLC and Citigroup are acting as joint book-running managers for the proposed offering.

The securities described above are being offered by Summit pursuant to a shelf registration statement on Form S-3, including a base prospectus, that was previously filed with the Securities and Exchange Commission (SEC) and which became automatically effective on June 9, 2026. A preliminary prospectus supplement and accompanying base prospectus relating to and describing the terms of the proposed offering will be filed with the SEC and will be available on the SEC’s website at www.sec.gov. Copies of the preliminary prospectus supplement and accompanying base prospectus may also be obtained, when available, from: J.P. Morgan Securities LLC, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, or by email at prospectus-eq_fi@jpmchase.com and postsalemanualrequests@broadridge.com; Goldman Sachs & Co. LLC, Attention: Prospectus Department, 200 West Street, New York, NY 10282, by telephone at (866) 471-2526, or by email at Prospectus-ny@ny.email.gs.com; or Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, or by telephone at (800) 831-9146.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Summit Therapeutics

Summit Therapeutics Inc. is a biopharmaceutical oncology company focused on the discovery, development, and commercialization of patient-, physician-, caregiver- and societal-friendly medicinal therapies intended to improve quality of life, increase potential duration of life, and resolve serious unmet medical needs.

Summit was founded in 2003 and our shares are listed on the Nasdaq Global Market (symbol “SMMT”). We are headquartered in Miami, Florida, and we have additional offices in Palo Alto, California, Princeton, New Jersey, Dublin, Ireland, and Oxford, UK.

For more information, please visit https://www.smmttx.com.

Forward-looking Statements

Any statements in this press release about uncertainties related to market conditions and statements regarding the timing, size and expected gross proceeds of the offering, the satisfaction of customary closing conditions related to the offering and sale of securities, the grant to the underwriters of an option to purchase additional shares and the Company’s ability to complete the offering, and other statements containing the words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “would,” and similar expressions, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by such forward-looking statements as a result of various important factors, including conditions affecting the capital markets and the satisfaction of closing conditions related to the proposed public offering, the grant to the underwriters of the option to purchase additional shares, timing and size of the proposed offering and Summit’s intended use of proceeds therefrom, general economic, industry, or political conditions, the results of our evaluation of the underlying data in connection with the development and commercialization activities for ivonescimab, the outcome of discussions with regulatory authorities, including the Food and Drug Administration, the uncertainties inherent in the initiation of future clinical trials, availability and timing of data from ongoing and future clinical trials, the results of such trials, and their success, and global public health crises, that may affect timing and status of our clinical trials and operations, whether preliminary results from a clinical trial will be predictive of the final results of that trial or whether results of early clinical trials or preclinical studies will be indicative of the results of later clinical trials, whether business development opportunities to expand the Company’s pipeline of drug candidates, including without limitation, through potential acquisitions of, and/or collaborations with, other entities occur, expectations for regulatory approvals, laws and regulations affecting government contracts and funding awards, availability of funding sufficient for the Company’s foreseeable and unforeseeable operating expenses and capital expenditure requirements and other factors discussed in the “Risk Factors” section of filings that the Company makes with the SEC. Any change to our ongoing trials could cause delays, affect our future expenses, and add uncertainty to our commercialization efforts, as well as to affect the likelihood of the successful completion of clinical development of ivonescimab. Accordingly, readers should not place undue reliance on forward-looking statements or information. In addition, any forward-looking statements included in this press release represent the Company’s views only as of the date of this release and should not be relied upon as representing the Company’s views as of any subsequent date. The Company specifically disclaims any obligation to update any forward-looking statements included in this press release. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to the business of the company in general, see the prospectus supplement and related prospectus for this offering as well as the Company’s Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and its other reports filed with the SEC.

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