Summit Therapeutics plc ( Summit or the Company ) SUMMIT THERAPEUTICS REPORTS FINANCIAL RESULTS FOR THE FIRST QUARTER ENDED 30 APRIL 2016 AND OPERATIONAL PROGRESS Oxford, UK, 2 June 2016 Summit Therapeutics plc (AIM: SUM

Summit Therapeutics plc

( Summit or the Company )

SUMMIT THERAPEUTICS REPORTS FINANCIAL RESULTS FOR THE FIRST QUARTER ENDED 30 APRIL 2016 AND OPERATIONAL PROGRESS

Oxford, UK, 2 June 2016 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 first quarter ended 30 April 2016.

Mr Glyn Edwards, Chief Executive Officer of Summit commented: Our programmes in DMD and CDI both have the potential to

significantly improve the current standards of care and are making good progress towards the patients who could benefit from their unique mechanisms of action. With the IND clearance for the expansion of PhaseOut DMD into the US, we are on track to

announce initial data that could potentially demonstrate the mechanism of ezutromid and utrophin modulation in patients with DMD in January 2017.

In CDI, data from our Phase 2 CoDIFy trial continue to support ridinilazole as a novel, highly selective antibiotic that could greatly reduce

recurrent disease. As this programme advances to Phase 3, we are exploring potential partnerships to leverage the most value for patients, shareholders and our Company.

Utrophin Modulation Programme for DMD

Ezutromid (formerly SMT C1100) Highlights

Utrophin Modulator Pipeline: Future Generation Development

Ridinilazole (formerly SMT19969) Highlights

Financial Highlights

About Summit Therapeutics

Summit is a biopharmaceutical company focused on the discovery, development and commercialization 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).

For more information, please contact:

Forward Looking Statements

Any statements in this press release about our future expectations, plans and prospects, including statements about clinical development and commercialisation

of our product candidates, the timing of clinical results, potential third-party collaborations 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 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, whether preliminary results from a clinical trial will be predictive of the final results of that trial or whether results of early clinical trials will be indicative of the results of later clinical

trials, expectations for regulatory approvals, availability of funding sufficient for our foreseeable and unforeseeable operating expenses and capital expenditure requirements and other factors discussed in the Risk Factors section of

filings that we make with the Securities and Exchange Commission, including our Annual Report on Form 20-F for the fiscal year ended 31 January 2016. In addition, any forward-looking statements included in this press release represent our views

only as of the date of this release and should not be relied upon as representing our views as of any subsequent date. We specifically disclaim any obligation to update any forward-looking statements included in this press release.

Summit is seeking to treat all patients affected with the fatal disorder DMD using its utrophin modulation technology. Summit is also advancing a highly

selective antibiotic to treat CDI.

Summit s DMD utrophin modulation programme is a treatment approach independent of the underlying mutations in the

dystrophin gene that cause the disease. Therefore, this approach has the potential to benefit the entire patient population. Summit has established a leadership position in the field of utrophin modulation and is developing a pipeline of first,

second and future generation product candidates. Summit s most advanced utrophin modulator is ezutromid. It is an orally administered small molecule that is being evaluated in patient clinical trials. Ezutromid has received orphan drug

designation in the United States and Europe.

Summit s CDI therapy is ridinilazole, a novel class antibiotic that has the potential to treat the

initial infection and reduce recurrent disease, the key clinical issue in CDI. In the recent Phase 2 proof of concept clinical trial, ridinilazole markedly reduced recurrence rates and had a statistically superior rate of sustained clinical response

( SCR ) compared to vancomycin. Ridinilazole is now being prepared for Phase 3 clinical trials. Ridinilazole has received Qualified Infectious Disease Product, or QIDP, designation and has been granted Fast Track designation by the US Food

and Drug Administration ( FDA ).

Duchenne Muscular Dystrophy: Utrophin Modulation Programme

Ezutromid: Phase 2 Proof of Concept Trial

progressing into an open label Phase 2 proof of concept clinical trial. The 48-week open-label trial, called PhaseOut DMD, is expected to enrol up to 40 boys ranging in age from their fifth to their tenth birthdays. PhaseOut DMD aims to provide

proof of concept for ezutromid and utrophin modulation through measurements of muscle fat infiltration, as well as through measurements of utrophin protein and muscle fibre regeneration in muscle biopsies. A primary endpoint of the trial is the

change from baseline in magnetic resonance imaging parameters related to fat infiltration and inflammation of the leg muscles. Functional endpoints, including the six-minute walk test, North Star Ambulatory Assessment and patient reported outcomes,

are also being explored.

Summit expects to commence enrolment and dosing of patients in PhaseOut DMD at trial sites in the United Kingdom during the

second quarter of 2016. In late April 2016, the FDA cleared the investigational new drug application for ezutromid and enrolment into PhaseOut DMD at trial sites in the United States is expected to start during the third quarter of 2016. The Company

anticipates reporting data periodically during this trial with 24-week muscle biopsy data from the first group of patients enrolled expected to be reported in January 2017.

Ezutromid: Phase 1 New Formulation Trial

the current clinical development of ezutromid, Summit is conducting a Phase 1 clinical trial in heathy volunteers and patients with DMD to evaluate two potential optimised formulations of ezutromid. Interim data from this trial were reported in

The two new formulations were tested in healthy volunteers with one of these achieving an over ten-fold increase in blood plasma levels

compared to the current formulation of ezutromid. This formulation is now being evaluated in patients with DMD. Data from the initial dosing period showed all patients achieved drug levels within the range believed to be necessary for potential

therapeutic benefit. The initial dose tested was one tenth of that required with the current formulation to achieve similar drug concentration levels as those observed in the Phase 1b modified diet clinical trial. The Phase 1 new formulation trial

is now testing a higher dose of the new formulation, and firm decisions on the further development of this new formulation will await full data from the trial which are expected in the third quarter of 2016.

Utrophin Modulator Pipeline and Biomarker Development

part of the Company s strategy to maintain its leadership position in the field of utrophin modulation, Summit is advancing a pipeline of second and future generation utrophin modulators. The second generation molecules are structurally related

to ezutromid, but are designed to have more favourable pharmaceutical properties to achieve higher plasma levels of drug. Future generation molecules will likely be structurally distinct from ezutromid and second-generation molecules.

In March 2016, research was published in the peer reviewed journal PLoS ONE on the development of imaging

techniques designed to quantify utrophin protein and muscle fibre regeneration in muscle biopsies from patients with DMD and Becker muscular dystrophy ( BMD ), a milder form of muscular dystrophy. The developed assays allowed the absolute

quantification of regenerating muscle fibres within a biopsy section and, for the first time, the researchers observed a correlation between the percentage of regenerating muscle fibres with differences in clinical severity between patients with DMD

and BMD from whom the biopsy was taken.

Summit will host a Utrophin R&D Day on 15 June 2016 in New York City. The event is open to analysts, institutional investors and members of the press

and will feature presentations from three key opinion leaders in DMD alongside management. For more information, email investors@summitplc.com.

C. difficile Infection Programme

Phase 2 CoDIFy Clinical Trial

During the first quarter of

the fiscal year, further data were reported from a Phase 2 proof of concept clinical trial of ridinilazole called CoDIFy. CoDIFy was a double-blind, randomised active-control trial evaluating the efficacy of ridinilazole against the current standard

of care, the antibiotic vancomycin. CoDIFy enrolled 100 patients with half the patients receiving ten days of dosing with ridinilazole (200mg, twice a day), and half the patients receiving ten days of dosing with vancomycin (125mg, four times a

day). The trial was conducted in the United States and Canada.

CoDIFy met its primary endpoint with ridinilazole achieving a SCR rate of 66.7% compared

to 42.4% for vancomycin (non-inferiority margin of 15%, p=0.0004). This also represented statistical superiority of ridinilazole over vancomycin using the pre-specified 90% confidence interval. SCR was defined as clinical cure based on the

resolution of diarrhoea at the end of treatment and no recurrence of CDI within 30 days after the end of treatment. The difference in SCR was driven by a reduction in disease recurrence with ridinilazole having a recurrence rate of 14.3% compared to

34.8% with vancomycin. Cure rates at the end of treatment were 77.8% for ridinilazole compared to 69.7% for vancomycin.

In addition, preliminary analysis

of microbiome data from CoDIFy showed ridinilazole to be highly preserving of the gut microbiome. Patients treated with ridinilazole in CoDIFy exhibited no further damage to their microbiome during therapy with a proportion of patients showing

initial evidence of recovery of key bacterial groups that play a role in protecting from CDI. In contrast, patients treated with vancomycin suffered substantial damage to their gut microbiome during treatment and this persisted in many patients

during the 30-day post treatment period.

In CoDIFy, ridinilazole was generally well tolerated and the overall adverse event profiles of ridinilazole and

vancomycin were comparable. This primary analysis was conducted on the modified intent-to-treat, or mITT, population that comprised patients with CDI confirmed by the presence of free toxin and these results were consistent across all treatment

groups. Additional data from this trial are to be reported at the 2016 ASM Microbe conference which will be held June 16-20 in Boston, US.

of these positive data from CoDIFy, the Company is exploring options for the future development of ridinilazole, although the preference is to find a partner to advance ridinilazole to Phase 3 through commercialisation.

An exploratory Phase 2 clinical trial evaluating ridinilazole against the antibiotic fidaxomicin is currently ongoing in Europe and the US. The results from

this open label trial are expected to help inform the design of future Phase 3 clinical trials and the commercial positioning of ridinilazole. Top-line results from this trial are expected in the second half of 2016.

Preclinical Activities

In February 2016, data published in the Journal of Antimicrobial Chemotherapy reported that ridinilazole outperformed the current standards of care,

vancomycin and metronidazole, in preclinical studies by having a robust killing effect on C. difficile that significantly reduced the level of toxins produced by the bacteria that play a major role in driving the symptoms and severity of the

A composition of matter

patent covering ridinilazole was granted by the United States Patent and Trademark Office in April 2016. The patent (United States Patent 9,314,456) is entitled Antibacterial Compounds and provides a period of exclusivity for

ridinilazole in the United States until at least 1 December 2029, with the possibility of patent term extension.

The development of ridinilazole has

been financially supported by Seeding Drug Discovery and Translational Awards from the Wellcome Trust.

Other Operating Income

Other operating income for the

three months ended 30 April 2016 was 0.06 million compared to 0.4 million for the three months ended 30 April 2015. Income recognised as part of the Wellcome Trust Translational Award decreased by

0.2 million to 650 for the three months ended 30 April 2016 from 0.2 million for the three months ended 30 April 2015. As of 30 April 2016, we had an accrued income balance of 0.1 million

related to cash due to be received from the Wellcome Trust, which we expect to receive within the next twelve months upon achievement of the final milestone of the Wellcome Trust Award when we deliver final reports related to the grant. Income

recognized as part of the funding from Innovate UK for the DMD programme decreased by 0.1 million to 0.06 million for the three months ended 30 April 2016 from 0.2 million for the three months ended

30 April 2015. The decrease in income is in line with the achievement of milestones to date under the funding agreement.