Summit update on Phase 2 Trial for Ezumitrod November 2016 Oxford, UK, 16 November 2016 – Summit Therapeutics plc (NASDAQ: SMMT, AIM: SUMM), the drug discovery and development company advancing therapies for Duchenne muscular dystrophy (‘DMD’) and Clostridium difficile infection, today announces that it has enrolled its first patients at trial sites in the US into PhaseOut DMD, a Phase 2 proof of concept clinical trial of ezutromid in patients with DMD. Ezutromid dosing is expected to follow within a screening period of up to 28 days. Enrolment and dosing of patients into PhaseOut DMD in the UK is ongoing. Ezutromid is a utrophin modulator and represents a potential disease modifying treatment for all patients with DMD. “Ezutromid has shown great promise in preclinical testing as a universal treatment that has the potential to slow or stop disease progression in all patients with DMD, regardless of their underlying dystrophin gene mutation,” said John Jefferies, MD, of Cincinnati Children’s Hospital Medical Center, and the US coordinating investigator in PhaseOut DMD. “We are excited to participate in PhaseOut DMD and contribute to the clinical development of this utrophin modulator.” Ralf Rosskamp, MD, Chief Medical Officer of Summit added, “Our PhaseOut DMD clinical trial is an important component of bringing ezutromid to patients and families who are in urgent need of a disease modifying therapy, and we are making progress with patient enrolment in this clinical trial, with enrolment ongoing in the UK and now in the US.” This announcement contains inside information for the purposes of Article 7 of EU Regulation 596/2014 (MAR). About PhaseOut DMD PhaseOut DMD aims to provide proof of concept for ezutromid and utrophin modulation by measuring muscle fat infiltration, as well as by measuring utrophin protein and muscle fibre regeneration in muscle biopsies. The primary endpoint of the open-label trial is the change from baseline in magnetic resonance imaging parameters related to fat infiltration and inflammation of the leg muscles. Exploratory endpoints include the six-minute walk distance, the North Star Ambulatory Assessment and patient reported outcomes. PhaseOut DMD is a 48-week open-label trial expected to enrol up to 40 boys ranging in age from their fifth to their tenth birthdays at sites in the UK and the US. Each patient will receive two biopsies, one at baseline and the second either at 24 or 48 weeks. Data from the initial group of 24-week biopsies are expected Q2/Q3 2017. Further information is available at: https://clinicaltrials.gov/ct2/show/NCT02858362 and www.utrophintrials.com. About Utrophin Modulation in DMD DMD is a progressive muscle wasting disease that affects around 50,000 boys and young men in the developed world. The disease is caused by different genetic faults in the gene that encodes dystrophin, a protein that is essential for the healthy function of all muscles. There is currently no cure for DMD and life expectancy is into the late twenties. Utrophin protein is functionally and structurally similar to dystrophin. In preclinical studies, the continued expression of utrophin has a meaningful, positive effect on muscle performance. Summit believes that utrophin modulation has the potential to slow down or even stop the progression of DMD, regardless of the underlying dystrophin gene mutation. Summit also believes that utrophin modulation could potentially be complementary to other therapeutic approaches for DMD. The Company’s lead utrophin modulator, ezutromid, is an orally administered, small molecule. DMD is an orphan disease, and the US Food and Drug Administration (‘FDA’) and the European Medicines Agency have granted orphan drug status to ezutromid. Orphan drugs receive a number of benefits including additional regulatory support and a period of market exclusivity following approval. In addition, ezutromid has been granted Fast Track designation and Rare Pediatric Disease designation by the FDA. About Summit Therapeutics Summit is a biopharmaceutical company focused on the discovery, development and commercialisation of novel medicines for indications for which there are no existing or only inadequate therapies. Summit is conducting clinical programs focused on the genetic disease Duchenne muscular dystrophy and the infectious disease C. difficile infection. Further information is available at www.summitplc.com and Summit can be followed on Twitter (@summitplc). Forward-looking Statements Any statements in this press release about Summit’s future expectations, plans and prospects, including but not limited to, statements about the clinical and preclinical development of Summit’s product candidates, the therapeutic potential of Summit’s product candidates, and the timing of initiation, completion and availability of data from 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 on-going and future clinical trials and the results of such trials, 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, availability of funding sufficient for Summit’s foreseeable and unforeseeable operating expenses and capital expenditure requirements and other factors discussed in the "Risk Factors" section of filings that Summit makes with the Securities and Exchange Commission including Summit’s Annual Report on Form 20-F for the fiscal year ended January 31, 2016. 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 Summit’s views only as of the date of this release and should not be relied upon as representing Summit’s views as of any subsequent date. Summit specifically disclaims any obligation to update any forward-looking statements included in this press release.