1 Longer-Term Follow-Up of Western Patients Showed Improving, Favorable Trend in Overall Survival in Global Phase III HARMONi Clinical Trial for Ivonescimab Plus Chemotherapy in 2L+ EGFRm NSCLC With Longer-Term Follow-Up of Western Patients, Ivonescimab Plus Chemotherapy Demonstrated Improving Global OS Trend with Nominal p-value of 0.0332 vs. Chemotherapy Alone; North American Patients’ OS HR=0.70 Consistent Median Overall Survival Observed in Western, Asian Patients in Longer-Term Follow-Up Analysis of Western Patients Presented at Presidential Symposium at WCLC 2025 Conference Call to be Held at 8:00am ET on Monday, September 8, 2025 Miami, Florida, September 7, 2025 – Summit Therapeutics Inc. (NASDAQ: SMMT) ("Summit," "we," or the "Company") today announced data from the Phase III HARMONi trial featuring the novel, potential first-in-class investigational bispecific antibody, ivonescimab. The data was presented this morning as part of the Presidential Symposium at the International Association for the Study of Lung Cancer’s (IASLC) 2025 World Conference on Lung Cancer (WCLC 2025) in Barcelona, Spain. The HARMONi presentation, Ivonescimab vs Placebo Plus Chemo, Phase 3 in Patients with EGFR+ NSCLC Progressed with 3rd gen EGFR-TKI Treatment: HARMONi, evaluated ivonescimab plus platinum-doublet chemotherapy compared to placebo plus platinum-doublet chemotherapy in patients with epidermal growth factor receptor (EGFR)-mutated, locally advanced or metastatic non-squamous non-small cell lung cancer (NSCLC) who have progressed after treatment with a 3rd generation EGFR tyrosine kinase inhibitor (TKI). This is a clinical setting with a patient population where PD-1 monoclonal antibodies have previously been unsuccessful in Phase III global clinical trials in showing either a progression-free survival (PFS) or overall survival (OS) benefit, the two primary endpoints of this clinical study. The trial results were presented by Jonathan Goldman, MD, Professor of Medicine at UCLA in the Hematology/Oncology Division, UCLA Director of Clinical Trials in Thoracic Oncology, Associate Director of Early Drug Development, and Chair of University of California Lung Cancer Consortium. Clinically Meaningful Efficacy As previously disclosed, ivonescimab in combination with chemotherapy showed a positive trend in OS in the primary analysis without achieving a statistically significant benefit with a hazard ratio of 0.79 (95% CI: 0.62 – 1.01; p=0.057). The statistical analysis plan for the study required a p-value of 0.0448 in order to achieve statistical significance at the time of the primary analysis of overall survival. Median overall survival was 16.8 months for those patients administered ivonescimab plus chemotherapy vs. 14.0 months for those receiving placebo plus chemotherapy. It was noted at the time of the primary analysis that the median follow-up time for western patients was 9.2 months and less than the median overall survival at the time of the primary analysis, and these patients may continue to be followed for long-term outcomes.

2 Primary Analysis (DCO: Apr 2025) Ivonescimab + Chemo (n=219) Placebo + Chemo (n=219) Median Overall Survival, ITT 16.8 mos 14.0 mos Hazard Ratio 0.79 (95% CI: 0.62 – 1.01; p=0.057) DCO = data cut-off; ITT = intention to treat population; mos = months In September 2025, an additional analysis was performed, whereby the western patients were followed to increase their time on study (Asian patients were locked at the time of the primary analysis). In this analysis that included longer-term follow-up of western patients (median follow-up time of western patients of 13.7 months), a hazard ratio consistent with the primary analysis was observed with an improved nominal p-value (HR=0.78; 95% CI: 0.62 – 0.98; nominal p=0.0332). Median OS for this analysis remained the same in both arms from the primary analysis. Median OS in western patients receiving ivonescimab was 17.0 months compared to 14.0 months for those receiving placebo (HR=0.84); median OS in North American patients, specifically, had not yet been reached in the ivonescimab arm compared to 14.0 months in the placebo arm (HR=0.70). The hazard ratios for western patients in totality, as well as patients from the North American and European regions individually, improved from the primary OS analysis to the analysis with longer-term follow-up of western patients. Consistent benefit was observed across pre-defined subgroups. Longer-Term Follow-Up of Western Patients Analysis (DCO: Sept 2025) Ivonescimab + Chemo Placebo + Chemo Median Overall Survival, ITT 16.8 mos (n=219) 14.0 mos (n=219) Hazard Ratio, ITT 0.78 (95% CI: 0.62 – 0.98; nominal p=0.0332) Median Overall Survival, Western 17.0 mos (n=83) 14.0 mos (n=82) Hazard Ratio, Western 0.84 Median Overall Survival, N. America Not Reached (n=43) 14.0 mos (n=50) Hazard Ratio, N. America 0.70 Median Overall Survival, Asia 16.7 mos (n=136) 14.0 mos (n=137) Hazard Ratio, Asia 0.76 DCO = data cut-off; ITT = intention to treat population; mos = months Note: North American patients are a subset of Western patients. As previously disclosed at the prespecified primary data analysis for PFS, ivonescimab in combination with chemotherapy demonstrated a statistically significant and clinically meaningful improvement with a hazard ratio of 0.52 (95% CI: 0.41 – 0.66; p<0.00001). PFS was measured by blinded independent central radiology review committee (BICR) compared to placebo in combination with chemotherapy. Median PFS for ivonescimab vs. placebo plus chemotherapy was 6.8 months vs. 4.4 months, respectively. The PFS analysis was event driven and was conducted with 345 patients enrolled. There was a consistent observed benefit across pre-defined subgroups. In a longer-term follow-up of PFS, which included all western patients and at least six months of follow-up time for all patients, ivonescimab plus chemotherapy demonstrated a consistent, clinically meaningful improvement in PFS

3 with an observed HR of 0.57 (95% CI: 0.46 – 0.71). With the longer-term follow-up analysis, a consistent benefit in western vs. Asian patients was observed, as well as in patients with tumors with either PD-L1 positive or negative expression. This longer-term follow-up analysis of PFS was performed at the time of the primary OS analysis. Overall response rates were higher in the ivonescimab arm (45%) vs. the placebo arm (34%); median duration of response was longer in those patients administered ivonescimab plus chemotherapy (7.6 months) compared to those receiving placebo and chemotherapy (4.2 months). “The positive results from the HARMONi study underscore the global applicability of ivonescimab and demonstrates the potential benefit ivonescimab has to bring to patients around the world, including the United States,” stated Robert W. Duggan, Chairman and Co-Chief Executive Officer of Summit. “We appreciate that the US FDA worked together with us in order to continue this trial from the single-region into this multiregional setting for which we are sharing detailed results today, bringing ivonescimab closer to the forefront for patients in need globally.” Manageable, Consistent Safety Profile Ivonescimab in combination with chemotherapy demonstrated an acceptable and manageable safety profile, which was consistent with previous studies. Ivonescimab plus chemotherapy was well-tolerated with no new safety signals and comparable rates of discontinuation and death between both arms. There were 16 patients (7.3%) who discontinued ivonescimab due to treatment-related adverse events (TRAEs) compared to 11 patients (5.0%) who discontinued placebo due to TRAEs. There were four patients (1.8%) in the ivonescimab plus chemotherapy arm and five patients (2.3%) in the chemotherapy alone arm who died as a result of TRAEs in this Phase III study. The most frequent TRAEs for ivonescimab in combination with chemotherapy were anemia and decreases in white blood cell count, neutrophil count, and platelet count. Of note, less than 1% of patients in the ivonescimab plus chemotherapy arm experienced Grade 3 or higher hemorrhage (bleeding) events. Ivonescimab + Chemo (n=219) Placebo + Chemo (n=219) TRAEs Grade 3+ 50.0% 42.2% TRAEs Leading to Drug Discontinuation 7.3% 5.0% TRAEs Leading to Death 1.8% 2.3% Grade 3+ Immune-related 9.6% 6.0% Grade 3+ Possibly VEGF-related 7.3% 3.2% “With the results from HARMONi and continued upcoming catalysts from further HARMONi-2 and HARMONi-6 readouts, ivonescimab is well positioned to begin to realize its potential in changing the worldwide treatment landscape for cancer patients,” stated Dr. Maky Zanganeh, President and Co-Chief Executive Officer of Summit. “But to focus on today and the presentation of the HARMONi trial, we would like to reiterate our sincere gratitude to the patients, physicians, nurses, and caregivers who participated in and regulatory authorities who supported

4 this clinical study. Without the dedication of our investigators and courage of the patients willing to participate in clinical trials, it would be impossible to bring the potential next generation of therapies to those with cancer.” Conference Call Summit Therapeutics Inc. will host a conference call and live webcast to discuss recent updates related to ivonescimab, including data released at WCLC, on Monday, September 8, 2025 at 8:00am ET. Conference call and webcast information will be accessible through our website www.smmttx.com. An archived edition of the webcast will be available on our website later in the day on Monday. 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 2,800 patients have been treated with ivonescimab in clinical studies globally. Summit began its clinical development of ivonescimab in non-small cell lung cancer (NSCLC), commencing enrollment in 2023 in two multiregional Phase III clinical trials, HARMONi and HARMONi-3. Additionally, in early 2025, the Company began enrolling 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). 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 or non- squamous NSCLC, irrespective of PD-L1 expression. 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.

5 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. 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. 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,

6 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, the Company’s estimates regarding stock-based compensation, 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" and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” sections 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. Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved

Summit Therapeutics WCLC Update Call September 8, 2025 8:00am ET

Forward Looking Statement 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, the Company’s estimates regarding stock-based compensation, 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" and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” sections 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. Summit Confidential & Proprietary Information Do Not Copy or Distribute Presentation Summit Therapeutics WCLC Update Call - September 2025 2 Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Ivonescimab vs Placebo Plus Chemo, Phase 3 in Patients with EGFR+ NSCLC Progressed with 3rd gen EGFR-TKI Treatment: HARMONi Jonathan W. Goldman1, Antonio Passaro2, Janessa Laskin3, Delvys Rodrigues-Abreu4, Antonio Calles5, Lyudmila Bazhenova6, Giuseppe Lo Russo7, Natasha Leighl8, Frederico Cappuzzo9, Nicolas Girard10, Sanjay Popat11, Wenfeng Fang12, Yongzhong Luo13, Runxiang Yang14, Wenting Li15, Jianling Li16, Lori Styles16, Benjamin Thompson16, Li Zhang17, Xiuning Le18. 1UCLA Health, Santa Monica, CA, USA; 2European Institute of Oncology, Milan, Italy; 3British Columbia Cancer Research Institute, Vancouver, Canada; 4Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain; 5Hospital General Universitario Gregorio Marañón, Madrid, Spain; 6UC San Diego Moores Cancer Center, San Diego, CA, USA; 7Fondazione IRCCS Istituto Nazionale Tumori, Milan, Italy; 8Princess Margaret Cancer Centre University of Toronto, Toronto, Ontario, Canada; 9Regina Elena National Cancer Institute, Rome, Italy; 10Institut Curie, Paris, France; 11Lung Unit, Royal Marsden Hospital, London, UK; 12Sun Yat-sen University Cancer Center, Guangzhou, China; 13Hunan Cancer Hospital, Changsha, China; 14Yunnan Cancer Hospital, Kunming, China; 15Akeso Biopharma, Inc., Zhongshan, China; 16Summit Therapeutics, Menlo Park, CA, USA; 17Sun Yat-sen University Cancer Center, Guangzhou, China; 18The University of Texas MD Anderson Cancer Center, Houston, TX, USA. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Phase 3 Study Design Key Eligibility Criteria Locally advanced or metastatic NSCLC: • EGFR sensitizing mutation+ • Progressed on 3rd gen EGFR-TKI • ECOG 0 or 1 • Any PD-L1 expression Stratification factor by geographic region: • Brain metastases (yes or no) Ivonescimab + Chemotherapy (N = 219) Placebo + Chemotherapy (N = 219) Primary • OS, PFS by IRRC per RECIST 1.1 Secondary • ORR by IRRC, DoR, safety and tolerability Endpoints: Planned Efficacy Analyses • PFS primary (at ~231 events) & OS interim analyses • OS final analysis (at ~261 events) FPI: Jan 2022 (overall) LPI Asia: Nov 2022 LPI NA & EU (and overall): Oct 2024 Ivonescimab: 20 mg/kg Q3W Chemotherapy: • Carboplatin: AUC5 Q3W x 4 cycles (21 day/cycle) • Pemetrexed: 500 mg/m2 Q3W Note: Positive outcomes were reported from the single-region (Asia) study HARMONi-A, with PFS as the primary endpoint. R 1:1 N=438 DoR=duration of response; ECOG=eastern cooperative oncology group; EGFR= Epidermal growth factor receptor; EU=Europe; FPI=first patient in; IRRC= independent radiology review committee; LPI=last patient in; mets=metastases; NA=North America; ORR=overall response rate; OS=overall survival; NSCLC=non-small cell lung cancer; TKI=tyrosine kinase inhibitor; PD-L1= programmed cell death ligand; PFS=progression-free survival; Q3W=every 3 weeks; RECIST=response evaluation criteria in solid tumors. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Background Global Enrollment Time Period: Asia: Jan 2022 – Nov 2022 Western: May 2023 – Oct 2024 Timing of Global Analyses: PFS Primary Analysis: Jul 2024 PFS Total Analysis: Apr 2025 OS Primary Analysis: Apr 2025 OS Longer-term FU of Western pts* Analysis: Sep 2025 *For longer-term analysis for OS, western patients were followed to increase time on study; Asian patients were locked at the time of the primary OS analysis, having >30 mos of median FU time. PFS = progression-free survival; OS = overall survival; FU = follow-up Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Phase 3 Study Design Key Eligibility Criteria Locally advanced or metastatic NSCLC: • EGFR sensitizing mutation+ • Progressed on 3rd gen EGFR-TKI • ECOG 0 or 1 • Any PD-L1 expression Stratification factor by geographic region: • Brain metastases (yes or no) Ivonescimab + Chemotherapy (N = 219) Placebo + Chemotherapy (N = 219) Primary • OS, PFS by IRRC per RECIST 1.1 Secondary • ORR by IRRC, DoR, safety and tolerability Endpoints: Planned Efficacy Analyses • PFS primary (at ~231 events) & OS interim analyses • OS final analysis (at ~261 events) FPI: Jan 2022 (overall) LPI Asia: Nov 2022 LPI NA & EU (and overall): Oct 2024 Ivonescimab: 20 mg/kg Q3W Chemotherapy: • Carboplatin: AUC5 Q3W x 4 cycles (21 day/cycle) • Pemetrexed: 500 mg/m2 Q3W Note: Positive outcomes were reported from the single-region (Asia) study HARMONi-A, with PFS as the primary endpoint. R 1:1 N=438 DoR=duration of response; ECOG=eastern cooperative oncology group; EGFR= Epidermal growth factor receptor; EU=Europe; FPI=first patient in; IRRC= independent radiology review committee; LPI=last patient in; mets=metastases; NA=North America; ORR=overall response rate; OS=overall survival; NSCLC=non-small cell lung cancer; TKI=tyrosine kinase inhibitor; PD-L1= programmed cell death ligand; PFS=progression-free survival; Q3W=every 3 weeks; RECIST=response evaluation criteria in solid tumors. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Demographic and Baseline Characteristics Arms were well-balanced; majority were females, ECOG 1, never smokers; 25% with brain mets * Non-19del/L858R mutations include G719X, L861Q, S768I, etc. ECOG=eastern cooperative oncology group; EGFR= Epidermal growth factor receptor; TKI=tyrosine kinase inhibitor. Characteristic, n (%) Ivonescimab+chemo (N=219) Placebo+chemo (N=219) Age – Median (range) 62 (32-84) 60 (36-84) ≥65 yr 83 (37.9) 88 (40.2) Female 130 (59.4) 127 (58.0) Region – NA & Europe 83 (37.9) 82 (37.4) Asia 136 (62.1) 137 (62.6) Race – Asian 153 (69.9) 153 (69.9) White 51 (23.3) 54 (24.7) ECOG - 1 162 (74.0) 157 (71.7) Smoking - Never 143 (65.3) 155 (70.8) Stage - IV 215 (98.2) 214 (97.7) Brain metastasis 54 (24.7) 54 (24.7) Liver metastasis 32 (14.6) 23 (10.5) Prior line of systemic cancer therapy (median) 1.0 1.0 Prior EGFR-TKI 1st/2nd generation 95 (43.4) 92 (42.0) 3rd generation 219 (100) 218 (99.5) 4th generation 1 (0.5) 0 EGFR Mutation 19del 131 (59.8) 118 (53.9) L858R 74 (33.8) 90 (41.1) Non-19del/L858R* 15 (6.8) 11 (5.0) Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Primary Endpoint: PFS by IRRC Statistically significant and clinically meaningful benefit with ivonescimab Consistent PFS benefit by investigator: HR = 0.58 (95% CI: 0.45-0.73) 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 P F S ( % ) Ivonescimab+chemo Placebo+chemo 54.0% 34.7% 25.4% 8.3% median FU: 22.3 mo No. at risk Ivonescimab+chemo 172 134 76 48 34 24 16 10 5 0 Placebo+chemo 173 100 50 24 12 9 4 2 1 0 Months Events, n (%) Median (mo) HR (95% CI) P Value Ivonescimab+chemo 129 (75.0) 6.8 0.52 (0.41-0.66) <0.0001 Placebo+chemo 146 (84.4) 4.4 CI=confidence interval; FU=follow-up; HR=hazard ratio; IRRC= independent radiology review committee; PFS=progression-free survival. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

PFS by IRRC – Subgroup Analysis Consistent across pre-defined subgroups (Events/N)(Events/N) HRPbo + chemoIvo + chemo 0.52 (0.41-0.66) 0.50 (0.37-0.67) 0.61 (0.39-0.94) 0.60 (0.43-0.83) 0.49 (0.34-0.70) 0.30 (0.10-0.86) 0.56 (0.43-0.71) 0.34 (0.20-0.57) 0.59 (0.45-0.77) 0.58 (0.43-0.77) 0.47 (0.30-0.74) 0.48 (0.27-0.86) 0.54 (0.41-0.71) 0.54 (0.38-0.75) 0.51 (0.35-0.74) 0.35 (0.18-0.68) 0.69 (0.34-1.39) 0.52 (0.40-0.67) 0.1 0.5 1 2 146/173 101/110 45/63 74/92 72/81 12/36 134/137 34/42 112/131 101/121 45/52 33/43 113/130 69/86 73/78 17/21 15/20 131/153 129/172 89/115 40/57 74/97 55/75 6/36 123/136 28/41 101/131 95/117 34/55 19/35 110/137 77/104 45/56 25/27 19/26 110/146 Overall population Age Sex Geographic region Brain metastases prior to study entry Smoking history Baseline ECOG performance status Baseline EGFR mutation Liver metastases prior to study entry <65 years >=65 years Female Male NA & EU Asia Present Absent Never Former/Current 0 1 19Del L858R T790M Present Absent Ivonescimab + chemo Placebo + chemo Hazard Ratio (95% CI) Favors Ivonescimab + chemo Favors Placebo + chemo ECOG=eastern cooperative oncology group; EGFR= Epidermal growth factor receptor; IRRC= independent radiology review committee; PFS=progression-free survival; PS=performance status; TKI=tyrosine kinase inhibitor. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

PFS by Presence or Absence of Brain Mets 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 P F S ( % ) Ivonescimab+chemo Placebo+chemo Pts with Brain Mets at Baseline: HR = 0.34 (95% CI: 0.20-0.57) 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 P F S ( % ) Months Ivonescimab+chemo Placebo+chemo Pts with No Brain Mets at Baseline: HR = 0.59 (95% CI: 0.45-0.77) Months No. at risk Ivonescimab 41 30 15 7 6 4 2 1 0 +chemo Placebo 42 19 7 2 1 0 +chemo No. at risk Ivonescimab 131 104 61 41 28 20 14 9 5 0 +chemo Placebo 131 81 43 22 11 9 4 2 1 0 +chemo CI=confidence interval; HR=hazard ratio; PFS=progression-free survival; pts=patients. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

PFS by IRRC: Primary Analysis vs Total PFS Analysis Consistent PFS with Primary and Total (All Patients) PFS Analysis including all NA & EU patients 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 30 P F S ( % ) Months Ivonescimab+chemo Placebo+chemo Ivonescimab+chemo (LTF) Placebo+chemo (LTF) Primary analysis (median FU: 22.3 mo, N=345): HR = 0.52 (95% CI: 0.41-0.66) Total analysis (median FU: 29.7 mo, N=438): HR = 0.57 (95% CI: 0.46-0.71) • NA & EU: HR = 0.67 (95% CI: 0.45-1.00) (n=165) • Asia: HR = 0.55 (95% CI: 0.43-0.71) (n=273) Comparable PFS for PD-L1 pos and neg expression. PD-L1 status only required from NA & EU pts (n=160): • PD-L1 ≥1%: HR=0.55 (95% CI 0.33-0.91) (n=106) • PD-L1 <1%: HR=0.62 (95% CI 0.32-1.18) (n=54) (Primary) (Primary) CI=confidence interval; EU=Europe; FU=follow-up; HR=hazard ratio; IRRC=independent radiographic review committee; NA=North America; PD-L1= programmed cell death ligand; PFS=progression-free survival. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved. ( otal) (Total)

Primary Endpoint: Overall Survival Favorable Trend Observed; NA & EU Follow-up Not Yet Mature 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 30 33 36 39 O S ( % ) Months Ivonescimab+chemo Placebo+chemo Median FU: Overall mFU 29.7 mo • NA & EU mFU 9.2 mo No. at risk Ivonescimab+chemo 219 212 189 137 98 77 60 51 43 33 26 16 5 0 Placebo+chemo 219 210 186 132 92 63 52 44 38 30 18 9 0 CI=confidence interval; EU=Europe; FU=follow-up; HR=hazard ratio; NA=North America; OS=overall survival. Events, n (%) Median (mo) HR (95% CI) P Value Ivonescimab + chemo 122 (55.7) 16.8 0.79 (0.62-1.01) 0.0570 Placebo + chemo 140 (63.9) 14.0 Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved. No detrimental impact on any predefined subgroups

Overall Survival: Longer Term Western Follow-up OS stable with longer term Western Data, nominal p=0.0332 0 20 40 60 80 100 0 3 6 9 12 15 18 21 24 27 30 33 36 39 O S ( % ) Months Ivonescimab+chemo Placebo+chemo No. at risk Ivonescimab+chemo 219 212 190 160 127 92 68 53 43 33 26 16 5 0 Placebo+chemo 219 210 186 159 119 74 56 45 38 30 18 9 0 CI=confidence interval; EU=Europe; FU=follow-up; HR=hazard ratio; NA=North America; OS=overall survival; mo=months. Events, n (%) Median (mo) HR (95% CI) P Value Ivonescimab + chemo 134 (61.2) 16.8 0.78 (0.62-0.98) 0.0332 Placebo + chemo 157 (71.7) 14.0 Region Median FU (mo) Median OS (mo) NA & EU 13.7 17.0 vs. 14.0 NA 14.6 NR vs. 14.0 Asia 32.7 16.7 vs. 14.0 Data cutoff NA&EU: Sep 2025 Asia: Apr 2025 Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Overall Survival Subgroup Analysis – Longer Term FU Consistent across pre-defined subgroups ECOG=eastern cooperative oncology group; EGFR= Epidermal growth factor receptor;; NA = North America, EU = Europe, PS=performance status; TKI=tyrosine kinase inhibitor. Ivonescimab Placebo Favor Ivonescimab Favor Placebo Hazard Ratio + chemo + chemo + chemo + chemo (95% CI) (Events/N) (Events/N) 0.78 (0.62-0.98) 0.82 (0.62-1.09) 0.71 (0.48-1.05) 0.91 (0.67-1.23) 0.63 (0.44-0.91) 0.84 (0.53-1.32) 0.70 (0.38-1.30) 0.76 (0.58-0.99) 0.69 (0.43-1.09) 0.81 (0.62-1.06) 0.80 (0.61-1.05) 0.74 (0.48-1.13) 0.70 (0.42-1.17) 0.79 (0.61-1.03) 0.92 (0.67-1.25) 0.55 (0.37-0.82) 0.60 (0.31-1.15) 0.1 0.5 1 2 157/219 99/131 58/88 87/127 70/92 40/82 25/50 117/137 41/54 116/165 112/155 45/64 36/62 121/157 78/118 73/90 18/25 134/219 90/136 44/83 84/130 50/89 36/83 17/43 98/136 33/54 101/165 92/143 42/76 24/57 110/162 84/131 39/74 19/29 Overall population Age Sex Geographic region Brain metastases prior to study entry Smoking history Baseline ECOG performance status Baseline EGFR mutation <65 years >=65 years Female Male NA & EU NA* Asia Present Absent Never Former/Current 0 1 19Del L858R T790M Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved. *Provided for informational purposes; not a predefined subgroup

Reminder: Background Global Enrollment Time Period: Asia: Jan 2022 – Nov 2022 Western: May 2023 – Oct 2024 Timing of Global Analyses: PFS Primary Analysis: Jul 2024 PFS Total Analysis: Apr 2025 OS Primary Analysis: Apr 2025 OS Longer-term FU of Western pts* Analysis: Sep 2025 *For longer-term analysis for OS, western patients were followed to increase time on study; Asian patients were locked at the time of the primary OS analysis, having >30 mos of median FU time. PFS = progression-free survival; OS = overall survival; FU = follow-up Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Overall Response Rate and Duration of Response By IRRC 0% 20% 40% 60% 80% 100% Ivonescimab+chemo Placebo+chemo O R R /D C R 84% DCR 45% ORR 73% DCR 34% ORR CI=confidence interval; DCR=disease control rate; DoR=duration of response; ORR=overall response rate; IRRC= independent radiographic review committee. DoR (mo) Ivonescimab + chemo Placebo + chemo n 98 75 Median (95% CI) 7.6 (5.5-10.6) 4.2 (2.9-4.7) Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

2.3 0.9 10.1 2.8 1.8 1.4 19.3 12.4 1.4 12.8 2.8 0.9 12.4 0.9 0.5 0.5 16.5 6.4 11.0 50.0 42.2 27.1 31.2 49.1 17.4 17.4 24.8 15.1 28.0 42.7 32.6 20.6 45.0 28.4 26.1 56.4 10.1 11.9 17.9 10.6 28.0 42.2 28.0 18.8 44.0 95.0 93.1 GGT increased Constipation Asthenia Vomiting Decreased appetite Nausea ALT increased AST increased Platelet count decreased Neutrophil count decreased WBC count decreased Anemia Total 0% 20% 40% 60% 80% 100% Percent of Subjects (%) Treatment-Related Adverse Events (TRAEs) Most common were lab abnormalities, nausea, decreased appetite Grade ≥3 Ivonescimab + chemo Placebo + chemo Any Grade One patient in each treatment arm did not receive study drug TRAE, n(%) Ivonescimab + chemo (N=218) Placebo + chemo (N=218) Any Grade 207 (95.0) 203 (93.1) Grade ≥3 109 (50.0) 92 (42.2) Serious 61 (28.0) 33 (15.1) Led to d/c of ivonescimab/placebo 16 (7.3) 11 (5.0) Led to death 4 (1.8) 5 (2.3) Grade ≥3 irAE 21 (9.6) 13 (6.0) Grade ≥3 VEGF-related 16 (7.3) 7 (3.2) d/c=discontinuation; irAE=immune-related adverse events; VEGF= vascular endothelial growth factor. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

0.9 0.9 0.5 0.5 0.5 0.5 0.5 0.5 9.6 6.0 2.8 3.2 1.4 2.8 3.2 2.8 2.3 0.9 4.1 8.3 2.8 3.2 2.8 0.5 33.0 17.9 0 0 Creatinine increased Stomatitis Amylase increased Rash AST increased ALT increased Hyperthyroidism Hypothyroidism Total 0.5 0.9/1.4 0.9/0.9 0.5/0.5 1.8/2.8 1.4/2.8 0.9 3.7 0.9 0.9 7.3 3.2 10.6 1.8 13.3 3.7 13.8 7.3 33.5 15.1 0 0 Gastrointestinal Perforations and Fistula Congestive Heart Failure Arterial Thromboembolism Events (ATE) Venous Thromboembolic Events (VTE) Hemorrhage Hypertension Proteinuria Total 0% 20% 40% Percent of Subjects (%) Immune-related and VEGF-related TRAEs Most common irAEs: hypo/hyperthryroidism, transaminase elevation, rash; mostly low grade Most common VEGF-related TRAEs: proteinuria, hypertension, hemorrhage; mostly low grade VEGF-related irAE Pneumonitis/ILD, Ivo arm vs Pbo arm: 2.8% (1.4% Grade ≥3) vs 1.8% (1.4% Grade ≥3) Grade ≥3 Ivonescimab + chemo Placebo + chemo Any Grade 0% 20% Percent of Subjects (%) Grade ≥3 Ivonescimab + chemo Placebo + chemo Any Grade d/c=discontinuation; ILD=interstitial lung disease; irAE=immune-related adverse events; ivo=ivonescimab; pbo=pembrolizumab; TRAE=treatment-related adverse events; VEGF= vascular endothelial growth factor. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Summary • Ivonescimab had a significant and clinically meaningful PFS benefit in EGFRm+ NSCLC patients post-3rd gen TKI • Reduced risk of progression or death by 48% vs chemotherapy, HR=0.52 • Consistent efficacy across pre-defined subgroups • Increased ORR and DoR • OS final analysis showed favorable trend; HR=0.79 with p=0.0570 • Longer-term follow-up of Western patients showed stable OS; HR=0.78 with nominal p=0.0332 • Western patients’ median OS was numerically higher by 3 months • Ivonescimab well tolerated, with no new safety findings • <1% Grade 3+ bleeding and comparable rates of discontinuation and death between arms DoR=duration of response; EGFRm+=epidermal growth factor receptor mutation positive; EU=Europe; gen=generation; NA=North America; ORR=overall response rate; OS=overall survival; NSCLC=non-small cell lung cancer; TKI=tyrosine kinase inhibitor; PFS=progression-free survival. Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.

Acknowledgements Thank you to everyone who made this trial possible: • The patients and their families • The personnel at all the clinical study sites • The scientists, regulatory, operations, and other teams within Summit and Akeso who helped develop ivonescimab and supported the study Ivonescimab is an investigational therapy not presently approved by any regulatory authority other than China’s National Medical Products Administration (NMPA). Summit Therapeutics and the Summit Therapeutics logo are trademarks of Summit Therapeutics Inc. Copyright 2025, Summit Therapeutics Inc. All Rights Reserved.