1 Summit Therapeutics Reports Financial Results and Operational Progress for the First Quarter Ended March 31, 2025 Ivonescimab in Combination with Chemotherapy Achieves Statistically Significant Superiority in PFS vs. Tislelizumab (PD-1 Inhibitor) Plus Chemotherapy in First-Line Treatment of Patients with Advanced Squamous NSCLC in HARMONi-6 Study Conducted by Akeso in China Enrollment Continues in Global Phase III Trial HARMONi-3 in First-Line Treatment of Patients with Metastatic NSCLC Ivonescimab Receives Approval in China as Monotherapy for First-Line Treatment for Advanced NSCLC in Tumors with Positive PD-L1 Expression: Interim Overall Survival HR = 0.777 in China for HARMONi-2 Study Conducted by Akeso Enrollment Has Begun in HARMONi-7 Global Phase III Trial in First-Line PD-L1 High, Metastatic NSCLC Ivonescimab Collaborations Progressing in Multiple Solid Tumor Settings: MD Anderson Collaboration Begins Enrolling Two Clinical Trials; Additional ISTs Initiated and Enrolling Leadership Team Advanced with Appointment of Robert LaCaze as Chief Commercial Officer Miami, Florida, May 1, 2025 - Summit Therapeutics Inc. (NASDAQ: SMMT) ("Summit," "we," or the "Company") today reports its financial results and provides an update on its operational progress for the first quarter ended March 31, 2025. Operational & Corporate Updates Operational progress continues with ivonescimab (SMT112), an investigational, potentially first-in-class bispecific antibody combining the effects of immunotherapy via a blockade of PD-1 with the anti-angiogenesis effects associated with blocking VEGF into a single molecule: • In January 2023, we closed our Collaboration and License Agreement with Akeso Inc. (Akeso, HKEX Code: 9926.HK) for ivonescimab (SMT112), with which over 2,300 patients have been treated in clinical studies globally. Summit has rights to develop and commercialize ivonescimab in the United States, Canada, Europe, Japan, Latin America, including Mexico and all countries in Central America, South America, and the Caribbean, the Middle East, and Africa while Akeso retains development and commercialization rights for the rest of the world, including China. • Since in-licensing ivonescimab, we have begun our development for ivonescimab in non-small cell lung cancer (“NSCLC”), specifically launching Phase III clinical trials in the following proposed indications: ◦ HARMONi: Ivonescimab combined with chemotherapy in patients with epidermal growth factor receptor (EGFR)-mutated, locally advanced or metastatic non-squamous NSCLC who have progressed after treatment with a third-generation EGFR tyrosine kinase inhibitor (TKI)

2 ◦ HARMONi-3: Ivonescimab combined with chemotherapy in first-line metastatic NSCLC patients ◦ HARMONi-7: Ivonescimab monotherapy in first-line metastatic NSCLC patients with high PD-L1 expression • In October 2024, we completed enrollment in our HARMONi clinical trial. We expect to disclose topline results from HARMONi in mid-2025. Enrollment continues in HARMONi-3 and the initial patients have been enrolled in the US in HARMONi-7. • On April 23, 2025, our partner, Akeso, announced that the HARMONi-6 Phase III clinical trial met its primary endpoint of progression-free survival (PFS) at a prespecified interim analysis conducted by an Independent Data Monitoring Committee. This trial evaluated ivonescimab combined with platinum- based chemotherapy against tislelizumab, a PD-1 inhibitor, with the same chemotherapy regimen in patients with locally advanced or metastatic squamous NSCLC, regardless of PD-L1 expression. Conducted in China by our partners at Akeso, the trial showed statistically significant and clinically meaningful improvement in PFS for ivonescimab plus chemotherapy. Akeso noted that no new safety signals were identified. o This study is the first known Phase III trial in NSCLC to show significant improvement over a PD- (L)1 inhibitor combined with chemotherapy in a head-to-head setting. Following the success of Akeso’s HARMONi-2 study, this is the second instance where ivonescimab-based regimens have demonstrated a significant PFS benefit in front-line treatment in NSCLC. The full data set for HARMONi-6 is planned to be presented at an upcoming major medical conference later this year. • On April 25, 2025, Akeso announced that ivonescimab was approved in China by the National Medical Products Administration (NMPA), the Chinese Health Authority, for a second indication based on the results of the HARMONi-2 trial. HARMONi-2 evaluated monotherapy ivonescimab against monotherapy pembrolizumab in patients with locally advanced or metastatic NSCLC whose tumors have positive PD- L1 expression. HARMONi-2 is a single region, multi-center, Phase III study conducted in China sponsored by Akeso with all relevant data exclusively generated, managed, and analyzed by Akeso. o As a part of the review of the supplemental marketing application submitted by Akeso seeking a label expansion of ivonescimab in China, the NMPA requested that Akeso perform an interim analysis of overall survival (OS). Akeso announced that the results of this interim overall survival analysis included a clinically meaningful, strongly positive trend represented by a hazard ratio of 0.777. The analysis was conducted at 39% data maturity, with a nominal alpha level of 0.0001. • Ivonescimab clinical trial collaborations with leading organizations continue to progress and expand evaluating ivonescimab in solid tumor settings outside of metastatic non-small cell lung cancer. o As part of our strategic collaboration with MD Anderson, two clinical trials sponsored by MD Anderson began enrolling this past quarter in cutaneous squamous cell carcinoma and glioblastoma. o We continue to support investigator-sponsored trials (ISTs) beyond our work with MD Anderson; two ISTs have begun enrolling at the Memorial Sloan Kettering Cancer Center and the Dana Farber Cancer Institute.

3 o As we announced in February, our clinical trial collaboration with Pfizer will evaluate multiple antibody drug conjugates (ADCs) in combination with ivonescimab in unique solid tumor settings. The studies combining ivonescimab with Pfizer’s vedotin ADCs are planned to begin later this year. We plan to review the data generated from these clinical trials as a part of our consideration for advancing our clinical development for ivonescimab beyond non-small cell lung cancer. • In March, we further strengthened our leadership team with the appointment of Robert LaCaze as Chief Commercial Officer. Prior to joining Summit, Mr. LaCaze has held senior positions at major pharmaceutical companies including Executive Vice President and Head of the Oncology Strategic Business Unit overseeing the global oncology franchise at Bayer Healthcare and Senior Vice President and Head of Global Oncology at Bristol-Myers Squibb. He is a seasoned biopharmaceutical executive with over 30 years of extensive leadership experience in commercial strategy and execution. He has a proven track record of launching multi-billion-dollar products, building and growing blockbuster drug franchises, and expanding market presence for various oncology products. Financial Highlights Cash and Cash Equivalents & Short-term Investments • Aggregate cash and cash equivalents and short-term investments were $361.3 million and $412.3 million at March 31, 2025 and December 31, 2024, respectively. GAAP and Non-GAAP Research and Development (R&D) Expenses • GAAP R&D expenses according to generally accepted accounting principles in the U.S. (“GAAP”) were $51.2 million for the first quarter of 2025, compared to $30.9 million for the same period of the prior year. • Non-GAAP R&D expenses were $47.1 million for the first quarter of 2025, compared to $28.5 million for the same period of the prior year. GAAP and Non-GAAP General and Administrative (G&A) Expenses • GAAP G&A expenses were $15.6 million for the first quarter of 2025, compared to $11.5 million for the same period of the prior year. • Non-GAAP G&A expenses were $8.6 million for the first quarter of 2025, compared to $4.4 million for the same period of the prior year. GAAP and Non-GAAP Operating Expenses • GAAP operating expenses were $66.8 million for the first quarter of 2025, compared to $42.4 million for the same period of the prior year. • Non-GAAP operating expenses were $55.7 million for the first quarter of 2025, compared to $32.9 million for the same period of the prior year. The increase is primarily related to the increase in R&D expenses due to

4 expansion of clinical studies and development costs related to ivonescimab and increases in people costs as we continue to build out our team. GAAP and Non-GAAP Net Loss • GAAP net loss in the first quarter of 2025 and 2024 was $62.9 million or $(0.09) per basic and diluted share, and $43.5 million or $(0.06) per basic and diluted share, respectively. • Non-GAAP net loss in the first quarter of 2025 and 2024 was $51.8 million or $(0.07) per basic and diluted share, and $34.0 million or $(0.05) per basic and diluted share, respectively.

5 Use of Non-GAAP Financial Measures This release includes measures that are not in accordance with U.S. generally accepted accounting principles (“Non-GAAP measures”). These Non-GAAP measures should be viewed in addition to, and not as a substitute for, Summit's reported GAAP results, and may be different from Non-GAAP measures used by other companies. In addition, these Non-GAAP measures are not based on any comprehensive set of accounting rules or principles. Summit management uses these non-GAAP measures for internal budgeting and forecasting purposes and to evaluate Summit’s financial performance. Summit management believes the presentation of these Non-GAAP measures is useful to investors for comparing prior periods and analyzing ongoing business trends and operating results. For further information regarding these Non-GAAP measures, please refer to the tables presenting reconciliations of our Non-GAAP results to our U.S. GAAP results and the “Notes on our Non-GAAP Financial Information” that accompany this press release. First Quarter 2025 Earnings Call Summit will host an earnings call this afternoon, Thursday, May 1, 2025, at 4:30pm ET. The conference call will be accessible by dialing (800) 715-9871 (toll-free domestic) or (646) 307-1963 (international) using conference code 4936739. A live webcast and instructions for joining the call are accessible through Summit’s website www.smmttx.com. An archived edition of the webcast will be available on our website after the call. About Ivonescimab Ivonescimab, known as SMT112 in Summit’s license territories, North America, South America, Europe, the Middle East, Africa, and Japan, and as AK112 in China and Australia, is a novel, potential first-in-class investigational bispecific antibody combining the effects of immunotherapy via a blockade of PD-1 with the anti-angiogenesis effects associated with blocking VEGF into a single molecule. Ivonescimab displays unique cooperative binding to each of its intended targets with multifold higher affinity to PD-1 when in the presence of VEGF. This could differentiate ivonescimab as there is potentially higher expression (presence) of both PD-1 and VEGF in tumor tissue and the tumor microenvironment (TME) as compared to normal tissue in the body. Ivonescimab’s tetravalent structure (four binding sites) enables higher avidity (accumulated strength of multiple binding interactions) in the TME (Zhong, et al, SITC, 2023). This tetravalent structure, the intentional novel design of the molecule, and bringing these two targets into a single bispecific antibody with cooperative binding qualities have the potential to direct ivonescimab to the tumor tissue versus healthy tissue. The intent of this design, together with a half-life of 6 to 7 days after the first dose (Zhong, et al, SITC, 2023), is to improve upon previously established efficacy thresholds, in addition to side effects and safety profiles associated with these targets. Ivonescimab was engineered by Akeso Inc. (HKEX Code: 9926.HK) and is currently engaged in multiple Phase III clinical trials. Over 2,300 patients have been treated with ivonescimab in clinical studies globally. Summit has begun its clinical development of ivonescimab in non-small cell lung cancer (NSCLC), commencing enrollment in 2023 in two multi-regional Phase III clinical trials, HARMONi and HARMONi-3, and the Company has begun to enroll patients in the United States for HARMONi-7. HARMONi is a Phase III clinical trial which intends to evaluate ivonescimab combined with chemotherapy compared to placebo plus chemotherapy in patients with EGFR-mutated, locally advanced or metastatic non- squamous NSCLC who have progressed after treatment with a 3rd generation EGFR TKI (e.g., osimertinib).

6 Enrollment in HARMONi was completed in the second half of 2024, and top-line results are expected to be announced in the middle of this year. HARMONi-3 is a Phase III clinical trial which is intended to evaluate ivonescimab combined with chemotherapy compared to pembrolizumab combined with chemotherapy in patients with first-line metastatic, squamous and non-squamous NSCLC. HARMONi-7 is a Phase III clinical trial which is intended to evaluate ivonescimab monotherapy compared to pembrolizumab monotherapy in patients with first-line metastatic NSCLC whose tumors have high PD-L1 expression. In addition, Akeso has recently had positive read-outs in three single-region (China), randomized Phase III clinical trials for ivonescimab in NSCLC: HARMONi-A, HARMONi-2, and HARMONi-6. HARMONi-A was a Phase III clinical trial which evaluated ivonescimab combined with chemotherapy compared to placebo plus chemotherapy in patients with EGFR-mutated, locally advanced or metastatic non-squamous NSCLC who have progressed after treatment with an EGFR TKI. HARMONi-2 is a Phase III clinical trial evaluating monotherapy ivonescimab against monotherapy pembrolizumab in patients with locally advanced or metastatic NSCLC whose tumors have positive PD-L1 expression. HARMONi-6 is a Phase III clinical trial evaluating ivonescimab in combination with platinum-based chemotherapy compared with tislelizumab, an anti-PD-1 antibody, in combination with platinum-based chemotherapy in patients with locally advanced or metastatic squamous NSCLC, irrespective of PD-L1 expression. Ivonescimab is an investigational therapy that is not approved by any regulatory authority in Summit’s license territories, including the United States and Europe. Ivonescimab was initially approved for marketing authorization in China in May 2024, and its label was expanded in China in April 2025. Ivonescimab was granted Fast Track designation by the US Food & Drug Administration (“FDA”) for the HARMONi clinical trial setting. 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 Menlo Park, California, and Oxford, UK. For more information, please visit https://www.smmttx.com and follow us on X @SMMT_TX.

7 Contact Summit Investor Relations: Dave Gancarz Chief Business & Strategy Officer Nathan LiaBraaten Senior Director, Investor Relations investors@smmttx.com media@smmttx.com Summit Forward-looking Statements Any statements in this press release about the Company’s future expectations, plans and prospects, including but not limited to, statements about the clinical and preclinical development of the Company’s product candidates, entry into and actions related to the Company’s partnership with Akeso Inc., the Company's anticipated spending and cash runway, the therapeutic potential of the Company’s product candidates, the potential commercialization of the Company’s product candidates, the timing of initiation, completion and availability of data from clinical trials, the potential submission of applications for marketing approvals, potential acquisitions, statements about the previously disclosed At-The-Market equity offering program (“ATM Program”), the expected proceeds and uses thereof, 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 the Company’s ability to sell shares of our common stock under the ATM Program, the conditions affecting the capital markets, 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, 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 Securities and Exchange Commission. 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.

8 Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved

9 Summit Therapeutics Inc. GAAP Condensed Consolidated Statements of Operations (in millions, except per share data) Unaudited Three Months Ended March 31, 2025 2024 Operating expenses: Research and development $ 51.2 $ 30.9 General and administrative 15.6 11.5 Total operating expenses 66.8 42.4 Other income 3.9 2.0 Interest expense — (3.1) Net loss $ (62.9) $ (43.5) Net loss per share attributable to common shareholders per share, basic and diluted $ (0.09) $ (0.06) Summit Therapeutics Inc. GAAP Condensed Consolidated Balance Sheet Information (in millions) Unaudited March 31, 2025 December 31, 2024 Cash and cash equivalents and short-term investments $ 361.3 $ 412.3 Total assets $ 383.8 $ 435.6 Total liabilities $ 39.5 $ 46.8 Total stockholders' equity $ 344.3 $ 388.7