SUMMIT'S IND CLEARED BY FDA ALLOWING EXPANSION OF PhaseOut DMD, A PHASE 2 CLINICAL TRIAL OF EZUTROMID (SMT C1100), INTO THE US

• Enrolment of Patients with DMD in the US Expected to Start 3Q 2016
• Utrophin Modulation Offers Differentiated Approach in DMD

Oxford, UK 26 April 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, announces that the US Food and Drug Administration has cleared the Company's investigational new drug ('IND') application to expand the Phase 2 proof of concept clinical trial called PhaseOut DMD to trial sites in the US. PhaseOut DMD will evaluate the Company's lead utrophin modulator, ezutromid (formerly known as SMT C1100), in patients with DMD at sites in the UK and the US.

In contrast to many current therapeutic approaches to DMD, utrophin modulation has the potential to treat all boys and young men with DMD, regardless of their underlying dystrophin gene mutation.

"The IND clearance for PhaseOut DMD paves the way to expand PhaseOut DMD into the US and will provide access to a wider network of leading physicians in DMD as we seek to improve the lives of patients and families living with this devastating disease," said Ralf Rosskamp, MD, Chief Medical Officer of Summit. "PhaseOut DMD aims to show the potential benefits of ezutromid as a disease modifying approach for DMD for the first time in patients, and this approach could ultimately benefit the entire DMD patient population."

Summit expects to begin enrolling patients into US sites in the third quarter of 2016.

About PhaseOut DMD
PhaseOut DMD aims to provide proof of concept for ezutromid (SMT C1100) 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.

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 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.

*Ezutromid is the international nonproprietary name ('INN') recommended by the World Health Organization for SMT C1100. INNs, also known as generic names, are used globally to identify pharmaceutical substances.