Summit Therapeutics Publishes Scientific Updates to Corporate Website

Cambridge, MA, May 5, 2021 - Summit Therapeutics Inc. (NASDAQ: SMMT) today announced that we have updated the scientific and related content on our corporate website with respect to our investigational drug, ridinilazole, which is currently enrolling patients in its Phase 3 clinical trials.

The content provides scientific data in a consumable manner, summarizing the work performed to date with respect to ridinilazole, our precision antibiotic targeting C. difficile . It provides details surrounding the relationship between the human gut microbiome and recurrence of C. diff . infection. It also describes how ridinilazole has, thus far, shown a significant relative sparing of the microbiome compared to the broad-spectrum antibiotics that are the current standard of care for C. diff. treatment today.

We believe you will enjoy reading the content, and we look forward to your feedback as we continue on our important journey seeking regulatory approval for ridinilazole , with the goal of its use as first-line therapy to treat initial infection and reduce recurrence of C. diff. infection.

The specific content can be found at https://www.summittxinc.com/our-programmes/c-difficile-infection .

About C. difficile Infection Clostridioides difficile , or C. difficile, infection (CDI) is a bacterial infection of the colon that produces toxins causing inflammation of the colon and severe watery diarrhea, painful abdominal cramping, nausea, fever, and dehydration. CDI can also result in more serious disease complications, including bowel perforation, sepsis, and death. CDI is a contagious infectious disease that represents a serious healthcare issue in hospitals, long-term care homes, and the wider community. Summit estimates that there are approximately 500,000 cases of CDI each year across the United States based on a meta-analysis published in the Journal of Global Health , June 2019.

About Summit Therapeutics Summit Therapeutics, empowered by its Discuva Platform, the Company’s innovative antibiotic discovery engine, supported by BARDA and CARB-X funding, intends to be the leader in patient-friendly and paradigm-shifting innovation while being an ally to physicians. Our new mechanism antibiotics are designed to become the patient-friendly, new-era standard of care, by working in harmony with the human microbiome to treat prospective patients suffering from infectious disease, initially focusing on Clostridioides difficile infections (CDI). The overriding objective of Summit Therapeutics is to create value for patients, hospital infectious disease caregivers, and community-based infectious disease healthcare providers, as well as healthcare payers around the world. We seek to create value by developing drugs with high therapeutic efficacy - curing the cause of the patient's condition with minimal or zero disease recurrence or antimicrobial resistance, for the longest extent possible - and minimizing the trauma caused to the patient and healthcare ecosystem by minimizing serious side effects, disease recurrence, and inaccessibility to our treatments as a result of financial or other barriers. Currently, Summit’s lead product candidate, ridinilazole, is engaged in two pivotal global Phase 3 trials, Ri-CoDIFy 1 & 2, each enrolling approximately 680 patients vs. the standard of care (vancomycin) for the treatment and reduction of recurrence of C. difficile infections in addition to an adolescent trial, Ri-CoDIFy 3. Commercialization of ridinilazole for the treatment and the reduction of recurrence of CDI is subject to regulatory approvals.

For more information, please visit www.summittxinc.com and follow us on Twitter @summitplc. For more information on the Company’s Discuva Platform, please visit https://www.summittxinc.com/our-science/discuva-platform.

Contact Summit Investor Relations: Dave Gancarz Vice President, Investor Relations & Corporate Strategy [email protected]

General Inquiries: [email protected]

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, 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, the impact of the COVID-19 pandemic on the Company’s operations and clinical trials 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 uncertainties inherent in the initiation of future clinical trials, availability and timing of data from ongoing and future clinical trials and the results of such trials, global public health crises, including the coronavirus COVID-19 outbreak, 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, 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. 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.