Summit Therapeutics plc ( Summit , the Company or the Group ) SUMMIT THERAPEUTICS REPORTS FINANCIAL RESULTS FOR THE FOURTH QUARTER AND FISCAL YEAR ENDED 31 JANUARY 2017 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 2017 AND OPERATIONAL PROGRESS

Oxford, UK, 29 March 2017

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 fourth quarter and fiscal year ended 31 January 2017.

Mr Glyn Edwards, Chief Executive Officer of Summit, commented:

We believe the progress made over the past year in our DMD and CDI programmes, combined with our strengthened financial position following the signing of the Sarepta licensing agreement has placed us in a strong position to deliver

value for our patients and shareholders.

Our Phase 2 proof of concept trial, PhaseOut DMD, is well underway with enrolment expected to be

completed in the second quarter of 2017. We now look forward to providing the full analysis of 24-week biopsies from the approximately 20 patients dosed with the F3 or F6 formulation of ezutromid, plus 24-week MRI and functional measures from all patients in the trial, in the first quarter of 2018. This approach is in lieu of reporting interim analysis from a smaller group in 2017, and it is expected to provide a

more complete picture of the potential benefits of ezutromid at this time point on utrophin expression, muscle health and muscle function.

In CDI, our Phase 2 clinical data supports the potential front-line use of ridinilazole to treat the initial infection and provide patients with a

sustained clinical response. This sustained clinical response is the focus of our planned Phase 3 programme that is designed, with input from the FDA and EMA, to evaluate superiority of ridinilazole over the current standard of care antibiotic

vancomycin. With the Phase 3 trials planned to start in the first half of 2018, we look forward to an exciting and important time ahead as we seek to bring these two potentially important treatment options one step closer to patients.

Utrophin Modulation Programme for DMD

Licence and Collaboration Agreement

Ezutromid (formerly SMT C1100) Highlights

Ridinilazole (formerly SMT19969)

Financial Highlights

Conference Call and Webcast Information

a conference call and webcast to review the financial results for the fiscal year ended 31 January 2017 today at 1:00pm BST / 8:00am EDT. To participate in the conference call, please dial +44 (0)20 7136 2050(UK and international participants)

or +1 646 254 3361 (US local number) and use the conference confirmation code 1859782. 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).

For more information, please contact:

Forward Looking Statements

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

of our product candidates, the therapeutic potential of our product candidates, the timing of initiation, completion and availability of data from clinical trials, the potential benefits and future operation of the collaboration with Sarepta

Therapeutics Inc., including any potential future payments thereunder, any other 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.

CHAIRMAN S STATEMENT

The past year has been one of strong progress across the Company as we continue to advance our innovative drug programmes targeting rare and infectious

diseases. Our focus in rare diseases is on our utrophin modulator pipeline for the treatment of the fatal muscle wasting disease, Duchenne muscular dystrophy ( DMD ). In infectious diseases, we are developing a novel antibiotic called

ridinilazole for the treatment of patients with infections caused by the bacteria C. difficile.

A major highlight of the year was the signing of a

licence and collaboration agreement with Sarepta Therapeutics Inc. ( Sarepta ) for European rights to our utrophin modulator pipeline. This agreement provided a $40 million upfront cash payment to Summit with the potential for

substantial future success based milestone and royalty payments. The year also included positive clinical data in both our DMD and CDI programmes as we continue to progress these innovative therapies through clinical trials and towards potential

This progress leaves us poised for an exciting year ahead. This is expected to include the continuation of our

Phase 2 proof of concept trial for our lead utrophin modulator, ezutromid, and activities to prepare our novel antibiotic ridinilazole to be ready to enter Phase 3 clinical trials in the first half of 2018.

A Balanced Portfolio

I believe our pipeline of

investigational therapies provides a balanced risk profile. Our DMD programme aims to address the underlying cause of the disease by seeking to maintain production of utrophin protein to compensate for the dystrophin that is lacking in individuals

with DMD, in order to maintain healthy muscle function. We have shown the potential of this therapeutic approach in preclinical disease models and our focus is on demonstrating proof of concept in patients with DMD for ezutromid in the ongoing Phase

2 clinical trial called PhaseOut DMD. Generation of positive clinical data would clear a key technical milestone and support the continued development of ezutromid as a potential disease modifying treatment for this devastating muscle wasting

To complement this, our novel class antibiotic ridinilazole has already shown evidence of clinical efficacy in patients with CDI in our Phase 2

clinical trial. In my view, this leaves ridinilazole in a strong position to continue to progress to Phase 3 clinical development and towards potential regulatory approval, particularly in light of the historic clinical success of antibiotics that

have generated positive Phase 2 data.

Operational Progress: Sarepta Therapeutics Licence and Collaboration Agreement

A major achievement of the past year was signing the licence and collaboration agreement with Sarepta. This agreement granted Sarepta exclusive commercial

rights in Europe, Turkey and the Commonwealth of Independent States to our utrophin modulator pipeline, including our Phase 2 candidate ezutromid. In exchange, we benefited from a cash injection of $40 million with the potential for additional

development, regulatory and sales milestones that for ezutromid alone total up to $522 million, plus future sales royalties.

Summit a number of benefits. It provides access to additional development and regulatory expertise from Sarepta to support ezutromid and our wider utrophin pipeline while, importantly, we retained full commercial rights in other territories

including the United States.

Operational Progress: R&D overview

It is an important time ahead for both programmes. In DMD, we expect to conclude enrolment into PhaseOut DMD. This clinical trial is the first long-term study

conducted with a utrophin modulator, and aims to demonstrate proof of concept for ezutromid in patients with DMD. Proof of concept would represent a major technical milestone for our utrophin modulation programme and we look forward to reporting the

full 24-week data from this trial in the first quarter of 2018.

In parallel, we continue to develop our earlier

stage pipeline of future generation utrophin modulators. This pipeline shows our deep commitment to developing effective therapies for the DMD community. I look forward to reporting on the continued advance of this pipeline which is being developed

as part of our strategic alliance with the University of Oxford as we seek to maintain our leadership position in the field of utrophin modulation.

is an urgent need to develop new antibiotics to combat the serious healthcare threat posed by pathogens, including C. difficile. We continue to believe that ridinilazole offers the potential to change the treatment paradigm in CDI. Further

data we presented from our proof of concept Phase 2 trial showed ridinilazole was highly preserving of the gut microbiome in patients during treatment. This observation was in stark contrast to patients treated with the current standard of care

antibiotic vancomycin whose microbiomes were severely damaged during treatment. A damaged microbiome leaves patients at high risk from disease recurrence. We therefore believe ridinilazole has the potential to be positioned as the mainstay treatment

for CDI due to its potential to treat initial infection and reduce rates of recurrence.

Future Development Strategy

Our strategy for the future development of both programmes remains clear. In DMD, if any of our utrophin modulators receive marketing approval, we remain

committed to independently commercialising them in the United States, one of the world s most important pharmaceutical markets. Commercialisation options for the other territories not covered by the licence and collaboration agreement with

Sarepta continue to be evaluated.

As ridinilazole is prepared for entry into Phase 3 clinical trials, we are in parallel evaluating various options to

support its future development as we seek to maximise the value of this exciting asset. This includes a collaboration agreement with a third party, or securing substantial non-dilutive funding from government

entities or not for profit organisations. This evaluation will consider a number of factors as we seek to identify the optimal path to continue the development of ridinilazole.

To support the ongoing development of the

two programmes, the team was further strengthened during the year. This was highlighted by the full-time appointment of Dr David Roblin as our Chief Operating Officer and President of Research and Development. David has had an extensive and highly

successful career in the pharmaceutical industry that included holding senior management roles at Pfizer and Bayer. Most recently, David led the establishment of operations at the Francis Crick Institute in London as Chief Operating Officer.

David s broad expertise across all stages of drug development in many different therapeutic areas, including infectious diseases, will be invaluable to the wider team at Summit. David has been acting as a research and development adviser to

Summit since 2014, and we look forward to working with him as part of the Summit team in this role on a part-time basis starting in April 2017 before moving to full-time in June 2017. For Summit to have attracted an individual of David s

calibre and reputation is a reflection of the promise and innovation in our DMD and CDI programmes.

Summit has made strong progress with the programmes and the development of the business in 2016 and we look forward to an exciting year ahead. We will continue

with our proof of concept trial for ezutromid while activities to prepare ridinilazole for Phase 3 clinical trials continue.

I would like to thank all of

our shareholders for their continued support. I also wish to sincerely thank all the patients and their families who are involved with our clinical trials. Without their dedication and support, we would not be able to advance these potential new

treatments. Finally I would like to thank the team at Summit for the continued hard work over the past 12 months as we seek to advance potential new medicines that have the opportunity to transform the lives of patients and their families.

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 seeking to develop a treatment for all patients affected with the fatal disorder DMD using its utrophin modulation technology.

Summit s focus in infectious diseases is on advancing the development of an antibiotic called ridinilazole that has the potential to not only treat the initial CDI infection, but importantly to reduce rates of disease recurrence.

Duchenne Muscular Dystrophy: Utrophin Modulation Programme