Summit Therapeutics plc ( Summit , the Company or the Group ) Summit Therapeutics Reports Financial Results for the Fourth Quarter and Fiscal Year Ended 31 January 2018 and Operational Progress Conference Call Today at 1

Summit Therapeutics plc

( Summit , the Company or the Group )

Summit Therapeutics Reports Financial Results for the Fourth Quarter and Fiscal Year Ended 31 January 2018 and Operational Progress

Oxford, UK, and Cambridge, MA, US,

11 April 2018 Summit Therapeutics plc (NASDAQ: SMMT, AIM: SUMM) today reports its financial results for the fourth quarter and fiscal year ended 31 January 2018 and provides an update on operational progress.

Mr Glyn Edwards, Chief Executive Officer of Summit, commented: This was a landmark year for Summit s Duchenne muscular dystrophy

programme where we saw a statistically significant reduction in muscle damage and inflammation in patients after just 24-weeks of ezutromid treatment. This provides evidence that ezutromid is reducing the

severity of the disease for these patients.

Strongly encouraged by these findings, we are accelerating preparatory activities for a placebo

controlled trial of ezutromid and also preparing for a potential regulatory filing of ezutromid based on top-line data from the full 48-week results, which are expected

in the third quarter of 2018.

Our infectious disease business has also made major strides over the past year. With funding support from

BARDA, we are preparing to initiate our Phase 3 trials for ridinilazole, a precision antibiotic for the treatment of C. difficile infections. Based on the discovery and development platform we acquired in 2017, we are also building a pipeline of new

mechanism antibiotics as we position ourselves as leaders in the field of antibacterials.

With two lead clinical programmes in DMD and CDI,

and a growing pipeline of early-stage compounds, we are building a fully-integrated company focused on advancing novel mechanism drugs as new standards of care.

Financial Highlights

Conference Call and Webcast Information

a conference call and webcast to review the financial results for the fiscal year ended 31 January 2018 today at 1:00pm BST / 8:00am EDT. To participate in the conference call, please dial +44 (0)330 336 9411 (UK and international participants)

or +1 646 828 8156 (US local number) and use the conference confirmation code 1980085. Investors may also access a live audio webcast of the call via the investors section of the Company s website, www.summitplc.com. A replay of the

webcast will be available shortly after the presentation finishes.

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 programmes 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).

*Based on a conversion rate of US$1.4135 to 1.00

This announcement contains inside information for the purposes of Article 7 of EU Regulation 596/2014 (MAR).

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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, the timing of initiation, completion and availability of data from clinical trials, the potential submission of

applications for regulatory approvals, the sufficiency of Summit s cash resources, 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 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, 2017. 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.

CHAIRMAN S STATEMENT

This past year has been marked by success and progress across the business. Summit now has two clinical programmes with positive clinical data in patients,

external validation for both our C. difficile infection ( CDI ) and Duchenne muscular dystrophy ( DMD ) programmes, a strengthened pipeline for a sustainable future and a strengthened team to guide the development of novel

drugs for serious illnesses.

delivered the first clinical evidence of ezutromid activity in patients with DMD. Ezutromid has the potential to profoundly improve the lives of all patients living with DMD. The evidence we have seen after just 24 weeks of treatment indicates

ezutromid is potentially reducing the severity of the disease. To put the typical severity of the disease in perspective, patients with DMD progressively lose muscle function throughout their lives, ultimately resulting in premature death in their

late twenties. Changes to the inexorable disease progression could provide meaningful benefit for patients. We anticipate that the 48-week data has the potential to provide continued evidence of improved

disease progression through measurements of muscle health, and we expect to report those data in the third quarter of 2018.

The 24-week data have bolstered our confidence that ezutromid could become the standard of care for all patients with DMD. We are preparing ourselves to rapidly advance ezutromid towards the market after receipt of the 48-week data. We see two potential paths to get to market with positive 48-week data. In one scenario, we could potentially pursue accelerated approval in the US based on the 48-week data. In another scenario, we conduct a pivotal, placebo controlled trial that would be the basis of regulatory filings for approvals in the US and EU. Our recent fundraise in Europe allows us to maintain

clinical and regulatory flexibility for both of these options. We remain committed to independently commercialising ezutromid in the United States, one the world s most important pharmaceutical markets, while our partner, Sarepta Therapeutics,

has commercialisation rights in Europe.

Our precision antibiotic for CDI garnered third-party US Government support with a $62 million BARDA award. This is a major endorsement for ridinilazole.

These funds are helping to support the Phase 3 clinical and regulatory development of ridinilazole.

Ridinilazole s potential to treat CDI and reduce

recurrent disease make it an attractive potential option for front-line treatment. To support this positioning, we carefully designed our Phase 3 programme to provide evidence of value for patients, payors and healthcare providers. There is an

urgent need for new treatment options in CDI with over one million cases a year in the US and Europe and we believe ridinilazole is the answer.

external validation our CDI programme received this year from BARDA complements the validation we received of our DMD programme through our strategic partnership with Sarepta. This partnership continues to provide us with intangible benefits, such

as access to Sarepta s knowledge and expertise in DMD drug development, as well as financial support. This past year, we received a $22 million milestone payment from Sarepta upon the completion of enrolment in our PhaseOut DMD clinical

trial, and as of January 2018, Sarepta is contributing a 45% share of our global DMD programme development costs.

A Sustainable Pipeline

Antibiotic resistance is an emerging global health and political issue. We believe that our investments in antibiotic research and development provide an

opportunity for Summit to assume a leadership role in this field. Our strategy is to develop new mechanism antibiotics designed to treat specific diseases where we can demonstrate clear advantages over existing standards of care and have clear

commercial value. We will pursue this strategy with our recently acquired discovery and development platform.

Separately, we continue to secure our

leadership in utrophin modulation through our ongoing collaboration with the University of Oxford. We intend to have the first- and best-in-class molecules with the goal

of one day being able to stop DMD disease progression for all patients living with this disorder.

We enter this next year in a position of strength with great opportunities for our products. Our progress brought us one step closer to realising the

significant value of ezutromid and ridinilazole for the Company, shareholders and most importantly, patients. Our growth over the past year ensures we have a strong team and a pipeline for the future. We now look to an exciting year ahead with the

full results from PhaseOut DMD expected in the third quarter of this year.

Having two clinical stage assets with compelling patient data is a tremendous

achievement and one that would not have happened without the continued support from our shareholders and dedication and professionalism from our employees. Finally, I d like to thank the patients, families and clinical sites involved in our

clinical trials. Without them, we would not be able to make such progress in advancing our promising product candidates.

Frank Armstrong, FRCPE, FFPM

Non-Executive Chairman

Summit is a biopharmaceutical company focused on the discovery, development and commercialisation of novel medicines for indications in rare diseases and

infectious diseases for which there are no existing or only inadequate therapies. In rare diseases, Summit is pioneering utrophin modulation as a potential disease modifying treatment for all patients affected by the fatal disorder DMD. In

infectious diseases, Summit s clinical focus is on advancing the development of the precision antibiotic ridinilazole that has the potential to not only treat the initial CDI infection, but importantly to reduce rates of recurrent disease. In

the broader infectious disease area, Summit is developing new mechanism antibiotics against pathogens where an urgent unmet need exists, and where the Company can demonstrate advantages over current treatments.

Rare Diseases: Duchenne Muscular Dystrophy

Utrophin Modulation Programme

common and severe form of muscular dystrophy, impacting 50,000 patients in the developed world alone. DMD is caused by the lack of dystrophin, a protein that maintains healthy muscle function. The absence of dystrophin results in a catastrophic

cycle of muscle damage and repair that leads to progressive loss of functional ability and ultimately in premature death.

Utrophin and dystrophin play a

similar role in maintaining muscle function, but do so at different times. Utrophin plays this role when new muscle fibres are being formed, or when damaged fibres are being repaired, but then switches off to make way for dystrophin to perform this

role in mature muscle fibres. Since patients with DMD are not able to produce dystrophin, a cycle of muscle damage and repair occurs, which eventually leads to muscle fibre failure. Utrophin modulation aims to address the root cause of DMD by

maintaining the production of utrophin to substitute for the missing dystrophin. The presence of utrophin in mature muscle fibres could break the cycle of damage and repair and ultimately slow, or even stop, disease progression. Importantly, this

approach has the potential to treat all patients with DMD regardless of their underlying dystrophin gene mutation.

Summit has established a leadership

position in the field of utrophin modulation with a pipeline of small molecule utrophin modulator therapies. The Company s lead utrophin modulator, ezutromid, has shown evidence of reducing DMD disease severity in patients in a Phase 2 clinical

Ezutromid Clinical Development

PhaseOut DMD, a Phase 2 Proof of Concept Trial

PhaseOut DMD is a 48-week, open-label Phase 2 clinical trial

evaluating ezutromid in patients with DMD. The clinical trial completed enrolment of 40 patients aged between their fifth and tenth birthdays at multiple sites in the US and UK in May 2017. At the end of 48 weeks of dosing, patients have the option

of continuing to be dosed with ezutromid in an extension phase. Results from a planned 24-week interim analysis were announced in January and February 2018. Top-line

results from the full 48-week trial are expected in the third quarter of 2018.

PhaseOut DMD aims to establish

proof of concept for ezutromid through the evaluation of muscle health and function. Primary and secondary endpoints are focused on muscle health and exploratory measures assess muscle function. With respect to muscle health, PhaseOut DMD measures

the change from baseline in magnetic resonance parameters of the leg after 48 weeks of treatment as the primary endpoint. Biopsy measures evaluating utrophin and muscle damage are assessed as secondary muscle health endpoints. For muscle function,

PhaseOut DMD measures the North Star Ambulatory Assessment and six-minute walk distance.