Summit Therapeutics plc ( Summit or the Company ) SUMMIT THERAPEUTICS REPORTS FINANCIAL RESULTS FOR THE THIRD QUARTER ENDED 31 OCTOBER 2015 AND OPERATIONAL PROGRESS Oxford, UK, 17 December 2015 Summit Therapeutics plc (A

Summit Therapeutics plc

( Summit or the Company )

SUMMIT THERAPEUTICS REPORTS FINANCIAL RESULTS FOR THE THIRD QUARTER ENDED 31 OCTOBER 2015 AND OPERATIONAL PROGRESS

Oxford, UK, 17 December 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 third quarter ended 31 October 2015.

Mr Glyn Edwards, Chief Executive Officer of Summit commented: We have recently announced positive clinical trial results for

both our lead programmes in DMD and CDI, enabling us to advance these promising candidates to the next stage of clinical development. In DMD, our lead utrophin modulator, SMT C1100, is poised to enter a Phase 2 proof of concept trial after

demonstrating the ability to achieve exposure levels in patients that we believe may be able to sustain utrophin production and result in clinical benefit. Utrophin modulation has significant promise as a disease-modifying therapy for all patients

We also recently reported that in our Phase 2 trial in CDI that ridinilazole (SMT19969) achieved statistical superiority over

vancomycin in sustained clinical response in CDI, a significant global healthcare threat. Ridinilazole has shown great potential to address recurrent disease, the key clinical issue in the treatment of CDI, and we look forward to evaluating our

options for advancing this novel class antibiotic into Phase 3 trials as quickly as possible.

RECENT OPERATIONAL HIGHLIGHTS

Utrophin Modulation Programme for DMD:

SMT C1100 Highlights

(SMT19969) Highlights

FINANCIAL HIGHLIGHTS

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Summit is seeking to treat all boys and young men affected with the fatal disorder Duchenne muscular dystrophy ( DMD ) using its utrophin modulation

technology. Summit is also advancing a highly selective antibiotic to treat Clostridium difficile infection ( CDI ).

utrophin modulation programme is a treatment approach that is independent of the underlying mutations in the dystrophin gene that cause the disease. This approach therefore 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 robust pipeline of first-, second- and future-generation product candidates. Summit is preparing to advance its lead utrophin modulator, SMT C1100, into a

Phase 2 proof of concept clinical trial following the successful completion of a Phase 1b modified diet clinical trial in patients with DMD.

Summit s CDI therapy is ridinilazole (SMT19969), 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 achieved statistical superiority in sustained clinical response over the antibiotic vancomycin, the current standard of care in CDI.

Ridinilazole is now advancing into Phase 3 clinical development.

Duchenne Muscular Dystrophy: Utrophin Modulation Programme

Summit s most advanced utrophin modulator is SMT C1100. It is an orally administered small molecule that is being evaluated in patient clinical trials.

SMT C1100 has received orphan drug designation in the United States and Europe.

SMT C1100: Phase 1b Modified Diet Clinical Trial

In September 2015, Summit reported positive data from its Phase 1b modified diet clinical trial of SMT C1100 in patients with DMD. The clinical trial was

designed to monitor the impact on absorption of SMT C1100 in patients who followed a recommended diet with balanced proportions of fat, proteins and carbohydrates, and combined with consuming a small glass of full fat milk at the time of dosing.

The detailed analysis presented at the 20th World Muscle Society Congress showed that the modified

diet had a positive impact on blood plasma levels of SMT C1100. All twelve patients in the trial achieved plasma levels that Summit believes may be able to sustain utrophin protein expression based on in vitro data generated in myoblast cells

from DMD patients and human myotubes.

SMT C1100: Phase 2 Proof of Concept Trial

SMT C1100 is now progressing into an open label Phase 2 proof of concept clinical trial. This trial is expected to enrol up to 40 boys with DMD between the

ages of five and ten years old at sites in Europe and the United States. Planned endpoints are expected to include changes in the fat content of muscle and in muscle inflammation as measured by magnetic resonance imaging ( MRI ) of the leg

muscles, and measurements of utrophin protein and muscle fibre regeneration from muscle biopsies. It is planned that each patient will have two muscle biopsies: one baseline biopsy and a second biopsy either after 24- or 48-weeks of treatment.

Functional measures such as the six minute walk test and the North Star Ambulatory Assessment will also be assessed throughout the trial.

applied to the UK Medicines and Healthcare Regulatory Authority for regulatory approval, and in parallel is seeking consent from the UK Ethics Review Committee. It is anticipated that the first patients will be enrolled and dosed in early 2016. An

investigational new drug ( IND ) application is also expected to be submitted to the US Food and Drug Administration ( FDA ) to enable the trial to enrol patients in the United States.

Summit expects to report data from the first group of patients enrolled in the trial periodically from the

second half of 2016 onwards, with the first set of 24-week muscle biopsy data expected to be available before the end of 2016.

As 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 utrophin modulators are structurally related to SMT C1100 but are

designed to have more favourable pharmaceutical properties. In July 2015, positive preclinical efficacy data were published in the peer reviewed journal Human Molecular Genetics on one of Summit s second generation utrophin modulators.

The data showed it increased utrophin expression along the entire fibre length of slow- and fast-twitch muscles to increase muscle stability, which resulted in reduced regeneration and necrosis.

Summit also reported promising progress in the development of future generation utrophin modulators as part of its strategic alliance with research teams at

the University of Oxford. In December, Summit announced the nomination of two series of utrophin modulators, including one with a mechanism that is potentially distinct to SMT C1100, for progression into lead optimisation studies. This represented

achievement of the first research milestone as part of the alliance. Summit also announced it has extended its exclusive strategic alliance with the University of Oxford until November 2019, with an option to extend it by a further 12 months. As

part of the extension, Summit has committed to increased funding of the sponsored research programme to 0.83 million a year starting in November 2015.

In addition to the current clinical development of SMT C1100, Summit is working to identify a potential optimised formulation of this drug. The Company is

working with leading formulation companies and two potential formulations are in a Phase 1 clinical trial. Each formulation has been evaluated in healthy volunteers and the Company has selected one to be evaluated in patients with DMD.

C. difficile Infection Programme

CDI is a major healthcare threat with between 450,000 and 700,000 annual cases in the United States alone. Mainstay treatments are dominated by broad spectrum

antibiotics, the use of which is associated with high rates of recurrent disease. With each episode typically being more severe and associated with increased risk of mortality, recurrent disease is the key clinical issue in CDI. Ridinilazole

(SMT19969) is a novel class antibiotic that has the potential to treat the initial infection and to reduce the high rates of recurrent disease. Ridinilazole has received Qualified Infectious Disease Product, or QIDP, designation and has been granted

Fast Track status from the FDA.

Phase 2 Clinical Programme

In November 2015, Summit announced that ridinilazole displayed statistical superiority in sustained clinical response ( SCR ) over vancomycin in a

Phase 2 proof of concept clinical trial named 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.

The Phase 2 trial 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 statistical superiority in SCR with ridinilazole was driven by a large numerical

reduction in recurrent disease compared to vancomycin.

Ridinilazole was generally well tolerated and the overall adverse event profiles of the two antibiotics 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. It is expected that more detailed findings from this Phase 2 trial will be

reported during the first half of 2016.

An exploratory Phase 2 clinical trial evaluating ridinilazole against the antibiotic fidaxomicin is currently

on-going in the UK. The results from this open label trial are expected to help inform the design of the planned Phase 3 trials and commercial positioning of ridinilazole. Top-line results are expected during the first half of 2016.

The development of ridinilazole has been financially supported through to completion of this Phase 2 clinical trial milestone by Seeding Drug Discovery and

Translational Awards from the Wellcome Trust.

Other Operating Income

Other operating income for the

three months ended 31 October 2015 was 0.4 million compared to 0.5 million for the three months ended 31 October 2014. Other operating income for the nine months ended 31 October 2015 was

1.2 million compared to 1.6 million for the nine months ended 31 October 2014. Income recognised as part of the Wellcome Trust Translational Award was lower in both the three months ended 31 October 2015 and the

nine months ended 31 October 2015 as a result of a lower contribution rate ascribed to Phase 2 clinical trial activities as compared to Phase 1 clinical trial activities under the terms of the funding agreement. The Company has received

3.9 million out of the 4.0 million awarded by the Wellcome Trust to date. Income recognised as part of funding from Innovate UK for the DMD programme was lower in the three months ended 31 October 2105 and the nine

months ended 31 October 2015, in line with the achievement of milestones to date under the terms of the funding agreement. The Company was awarded up to 2.4 million in funding from Innovate UK and has received

1.6 million to date.

Research and Development Expenses

development expenses increased by 1.9 million to 4.5 million for the three months ended 31 October 2015 from 2.6 million for the three months ended 31 October 2014. Research and development expenses

increased by 4.2 million to 11.8 million for the nine months ended 31 October 2015 from 7.6 million for the nine months ended 31 October 2014. These increases reflected increased expenditure related to

the Company s CDI and DMD programme activities as well as an increase in staff related costs.

General and Administration Expenses

General and administration expenses increased by 0.7 million to 1.3 million for the three months ended 31 October 2015 from

0.6 million for the three months ended 31 October 2014. General and administration expenses increased by 0.3 million to 3.4 million for the nine months ended 31 October 2015 from 3.1 million

for the nine months ended 31 October 2014. The increases in both the three months ended 31 October 2015 and the nine months ended 31 October 2015 were driven by costs associated with being a publicly traded company in the US following

the Company s NASDAQ listing, as well as expenses associated with maintaining the Company s US office which opened in 2014. General and administration expenses in the nine months ended 31 October 2014 included a provision of

0.7 million for milestone payments paid to two US DMD patient groups as part of funding agreements recognised in July 2014.

Operating Activities

Net cash outflow from operating

activities increased by 3.6 million to 11.2 million for the nine months ended 31 October 2015 compared to a net cash outflow of 7.6 million for the nine months ended 31 October 2014. The increase in net

cash outflow was driven by an increase in operating expenses and working capital requirements, offset by the receipt of a research and development tax credit that increased by 0.7 million to 1.4 million for the nine months

ended 31 October 2015 from 0.7 million for the nine months ended 31 October 2014.