Summit Therapeutics plc ( Summit or the Company ) SUMMIT THERAPEUTICS REPORTS FIRST QUARTER RESULTS FOR THE THREE MONTHS ENDED 30 APRIL 2015 Oxford, UK, 11 June 2015 Summit Therapeutics plc (AIM: SUMM, NASDAQ: SMMT), the

Summit Therapeutics plc

( Summit or the Company )

THERAPEUTICS REPORTS FIRST QUARTER RESULTS FOR THE THREE MONTHS ENDED 30 APRIL 2015

Oxford, UK, 11 June 2015 Summit Therapeutics

plc (AIM: SUMM, NASDAQ: SMMT), the drug discovery and development company advancing therapies for Duchenne muscular dystrophy ( DMD ) and C. difficile infection ( CDI ), today reports its financial results for the three

months ended 30 April 2015.

Mr Glyn Edwards, Chief Executive Officer of Summit commented: During the first quarter, we substantially

expanded our shareholder base with a successful NASDAQ listing, which has provided significant support for the on-going patient clinical trials of our lead product candidates for the treatment of DMD and CDI. We look forward to reporting data from

these studies as we seek to establish the potential of our two programmes as life-changing treatments.

DUCHENNE MUSCULAR DYSTROPHY PROGRAMME

C. DIFFICILE INFECTION PROGRAMME

OPERATIONAL HIGHLIGHTS

FINANCIAL HIGHLIGHTS

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Summit is seeking to treat all boys affected with the fatal disease Duchenne muscular dystrophy using its pioneering utrophin modulation technology. Summit is

also advancing a highly selective antibiotic to treat Clostridium difficile infection.

Summit s DMD utrophin modulation programme is a

treatment approach that is independent of the underlying mutations in the dystrophin gene that cause the disease and therefore has the potential to address the entire population of DMD patients. Summit has established a leadership position in the

field of utrophin modulation with a robust pipeline of first-, second- and future-generation candidates. Summit is currently evaluating its most advanced product candidate, SMT C1100, in a Phase 1b clinical trial in DMD patients and, in parallel,

continuing development of second- and future-generation utrophin modulators.

Summit s CDI therapy in clinical development is SMT19969, an orally

administered small molecule antibiotic. SMT19969 is designed to selectively target Clostridium difficile bacteria without causing collateral damage to the healthy gut flora of patients, thereby reducing CDI recurrence rates, the key clinical

issue in this disease.

Nasdaq Listing and Equity Offering

In March 2015, Summit successfully completed a US initial public offering on the NASDAQ Global Market issuing 3,967,500 American Depositary Shares

( ADSs ) at an offering price of $9.90 per ADS. Total gross proceeds were $39.3 million.

The Company believes that its NASDAQ listing will

provide greater access to the large number of specialist healthcare investors in the US, as well as increase liquidity in the trading of its shares. The funds raised in the US IPO will support the on-going clinical development of both the

Company s utrophin modulation programme for the treatment of DMD and novel antibiotic for the treatment of CDI.

The ADSs trade on NASDAQ under the

symbol SMMT . The NASDAQ listing complements the listing of the Company s Ordinary Shares on AIM, a market of the London Stock Exchange. The Company s Ordinary Shares trade on AIM under the symbol SUMM . Each ADS

represents five Ordinary Shares of 1 pence each in the capital of the Company.

Duchenne Muscular Dystrophy: Utrophin Modulation Programme

SMT C1100: Lead Utrophin Modulator

utrophin modulator is SMT C1100. SMT C1100 is a small molecule currently being evaluated in a Phase 1b modified diet trial in patients with DMD.

modified diet trial is a randomised, placebo-controlled clinical trial that aims to increase the blood plasma levels of SMT C1100 compared to the blood plasma levels observed in the Company s previous open label Phase 1b trial completed in 2014

by providing patients with specific dietary guidance recommending balanced proportions of fat, protein and carbohydrates. The trial is also evaluating the potential impact of SMT C1100 on enzyme biomarkers that are related to muscle health and

further evaluating the safety and tolerability of the drug candidate.

The trial is now fully enrolled with 12 DMD patients between the ages of 5 and 13

years old. The blinded trial consists of three randomised 14-day treatment periods separated by washout periods of at least 14 days. Each patient will receive two different doses of SMT C1100 and a placebo control.

Summit expects to report top-line data from this trial in the third quarter of 2015.

SMT C1100: Future Clinical Trial Plans

modified diet trial is successful, Summit plans to initiate in the second half of 2015 a Phase 2 open label trial in DMD patients designed to evaluate the longer-term effects of SMT C1100 on muscle health, function and safety. Summit also plans to

initiate a larger, multinational Phase 2 placebo-controlled trial that is expected to include sites in the United States and Europe in early 2016.

highlighted by the on-going Phase 1b trial, the Company believes a balanced diet has the potential to improve blood plasma levels of SMT C1100. In parallel, the Company is developing an optimised formulation of SMT C1100 and is currently working to

identify and evaluate a number of potential formulations of SMT C1100 for their suitability to be advanced into human clinical trials.

Future-Generation Utrophin Modulators

As part of the Company s strategy to maintain its leadership position in the field of utrophin modulation

research, Summit is also advancing a pipeline of second- and future-generation utrophin modulators. The second-generation molecules are structurally related to SMT C1100, but are designed to have more favourable pharmaceutical properties to achieve

higher drug uptake. Future-generation molecules will likely be structurally distinct from SMT C1100 and second-generation molecules. Summit continues research in this area and will present data at upcoming medical conferences.

C. difficile Infection Programme

SMT19969 is a novel antibiotic currently being evaluated in a Phase 2 proof of concept clinical trial being conducted in the United States and Canada. This

trial, named CoDIFy, is a double-blind, randomised active-control trial evaluating the efficacy of SMT19969 against the current standard of care, the antibiotic vancomycin. CoDIFy will enrol up to 100 patients with half the patients receiving ten

days of dosing with SMT19969, and the remaining patients receiving ten days of dosing with vancomycin.

The primary endpoint of the trial is sustained

clinical response, which is defined as clinical cure based on the resolution of diarrhoea at the test of cure visit on day 12 and no recurrence of CDI within 30 days after the end of treatment. The trial will examine a number of secondary endpoints

including the safety and tolerability of SMT19969, and its impact on the gut flora of patients. Top-line results from this trial are expected to be reported in the second half of 2015.

During the first quarter of 2015, a key patent protecting the use of SMT19969 in the treatment of CDI was issued by the US Patent and Trademark Office. The

Company believes this patent significantly strengthens the intellectual property estate protecting the use of SMT19969.

The development of SMT19969

continues to be substantially supported by a 4.0 million Wellcome Trust Translational Award through to completion of the Phase 2 proof of concept clinical trial.

Operational and Board Update

In February, the Company received authority from shareholders to change its registered name from Summit Corporation plc to Summit Therapeutics plc.

Also in February, Mr David Wurzer was appointed to the Board as a Non-Executive Director. Mr Wurzer brings extensive experience in financial and business

matters related to the pharmaceutical and biotechnology industries having held a number of senior executive and board level positions.

Other Operating Income

income for the three months ended 30 April 2015 was 0.4 million compared to 0.6 million for the three months ended 30 April 2014. Income recognised as part of the Wellcome Trust Award was 0.2 million

lower for the three months ended 30 April 2015 as a result of a lower contribution rate ascribed to Phase 2 activities as compared to Phase 1 activities under the terms of the funding agreement.

Research and Development Expenses

Research and development expenses increased by 0.5 million to 3.1 million for the three months ended 30 April 2015 from

2.6 million for the three months ended 30 April 2014. This increase included a 0.4 million increase in costs in respect to clinical activities for the CDI programme and a 0.1 million increase in staff related

General and Administration Expenses

and administration expenses increased by 0.2 million to 1.1 million for the three months ended 30 April 2015 from 0.9 million for the three months ended 30 April 2014. This increase was primarily due to

additional corporate costs following the Company s NASDAQ listing and additional expenses associated with the US office which was opened last year.

Operating Activities

Net cash outflow from operating activities increased by 2.4 million to 3.9 million for the three months ended 30 April 2015

compared to 1.4 million for the three months ended 30 April 2014. This was driven by an increase in operating expenses and an increase in working capital requirements of 1.4 million.

Investing Activities

Net cash outflow from investing

activities for the three months ended 30 April 2015 and the three months ended 30 April 2014 includes the net amount of bank interest received on cash deposits less amounts paid to acquire property and equipment.

Financing Activities

Net cash inflow from financing

activities in both periods presented relates to proceeds received from the sale of the Company s equity securities. The Company received net proceeds of 22.0 million from the sale of equity securities during the three month period

ended 30 April 2015 compared with net proceeds of 20.7 million from the sale of equity securities during the three month period ended 30 April 2014.

Nasdaq Listing and Equity Offering

financial position was significantly strengthened following the announcement on 5 March 2015 of a US initial public offering on the NASDAQ Global Market in which the Company issued 3,450,000 ADSs at a price of $9.90 per ADS. On 18 March

2015, the underwriters exercised in full their

over-allotment option to purchase an additional 517,500 ADSs on the same terms. Total gross proceeds of $39.3 million were raised. Each ADS represents five Ordinary Shares, thus 19,837,500

Ordinary Shares were issued in the offering.

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 our future expectations, plans and prospects, including statements about the clinical development of our product

candidates, the timing of clinical results and expectations regarding the sufficiency of our cash balance to fund operating expenses and capital expenditures, 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