THIS ANNOUNCEMENT (INCLUDING THE APPENDIX) AND THE INFORMATION CONTAINED HEREIN IS RESTRICTED AND IS NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, IN WHOLE OR IN PART, DIRECTLY OR INDIRECTLY, IN, OR INTO ANY JURISDICTION

THIS ANNOUNCEMENT (INCLUDING THE APPENDIX) AND THE INFORMATION CONTAINED HEREIN IS RESTRICTED AND IS NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, IN WHOLE OR

IN PART, DIRECTLY OR INDIRECTLY, IN, OR INTO ANY JURISDICTION IN WHICH SUCH RELEASE, PUBLICATION OR DISTRIBUTION WOULD BE UNLAWFUL. THIS ANNOUNCEMENT IS FOR INFORMATION PURPOSES ONLY AND DOES NOT CONSTITUTE AN OFFER OR AN INVITATION TO ACQUIRE OR

DISPOSE OF ANY SECURITIES. YOUR ATTENTION IS ALSO DRAWN TO THE IMPORTANT NOTICES AT THE END OF THIS ANNOUNCEMENT.

Summit Therapeutics plc

( Summit , or the Company )

Announces a Proposed Subscription and Placing to Raise approximately $50.0 million and Notice of General Meeting

Oxford, UK, and Cambridge,

MA, US, 6 December 2019 Summit Therapeutics plc (AIM: SUMM, NASDAQ: SMMT), a leader in antibiotic innovation, announces a proposed fundraising (the Fundraising ) of approximately $50 million through a

subscription and placing of new ordinary shares and warrants to existing investors which is subject to certain shareholder approvals being obtained and certain customary closing conditions being satisfied. The transaction includes proposals to

restructure the Company s board of directors (the Board ) and to cancel the trading on AIM of the Company s ordinary shares. The Company s American Depositary Shares ( ADSs ) will remain listed on the Nasdaq Stock

Market ( Nasdaq ) where one ADS represent five ordinary shares.

Glyn Edwards, Chief Executive Officer of Summit, said: Patients need new and better antibiotics. Innovation is required to develop

distinctive new drugs that address the resistance crisis without damaging our healthy microbiomes. Summit sees a huge opportunity in the antibiotic space for precision drugs targeting specific bacteria. We have great technology and people at Summit

to bring forward potent antibiotics with the potential to deliver better outcomes for patients and healthcare systems.

It is great that Bob

Duggan is leading this much-needed investment into Summit that will support progression of our ambitious plans, including developing ridinilazole, our precision antibiotic for the treatment of C. difficile infection. We have the opportunity to show

that ridinilazole is superior to vancomycin in sustained cures of C difficile infection, is able to preserve the microbiome of patients and offers substantial benefits to payors by reducing costly recurrences.

Mr Robert W. Duggan added: Microbiome friendly treatments I believe are the future. I am delighted to be investing in, and working with, the

Summit team with the goal of developing ridinilazole as the new front-line treatment option for C. difficile infection that is also kind to the microbiome of patients. I see a bright future for Summit as a public company listed on Nasdaq and I look

forward to joining the board and working to deliver ridinilazole to patients.

Shareholder Approval and General Meeting Information

The Fundraising is not being underwritten and is conditional (amongst other things) upon the passing by the Company s shareholders

( Shareholders ) of a resolution to approve a waiver (the Rule 9 Waiver ), which has been granted by the Takeover Panel, of certain obligations that would otherwise arise on Mr Duggan in connection with the Subscription pursuant

to rule 9 of the City Code on Takeovers and Mergers (the City Code ). Shareholder approval of this resolution and other applicable resolutions relating to the issue of the Subscription Shares, the Placing Shares and the Investor Warrants,

together with the proposed cancellation of the Company s ordinary shares to trading on AIM (collectively, the Resolutions ) will be sought at a general meeting of the Company to be held at the offices of CMS Cameron McKenna Nabarro

Olswang LLP, at Cannon Place, 78 Cannon Street, London EC4N 6AF, at 10.30 a.m. on 23 December 2019 (the General Meeting ).

The Fundraising and the AIM Delisting are conditional (amongst other things) on the passing of all of the

Resolutions by Shareholders at the General Meeting.

A circular, including notice of the General Meeting, setting out (amongst other things) further

details on the Subscription, the Placing, the proposed restructuring of the Board and AIM Delisting, and the Resolutions to be proposed at the General Meeting (the Circular ) is expected to be uploaded to the Company s website and

posted to Shareholders later today.

Application will be made to the London Stock Exchange for the new ordinary shares to be issued pursuant to the

Subscription and the Placing to be admitted to trading on AIM. Subject to the satisfaction of all applicable conditions, admission of the Subscription Shares and the Placing Shares to trading on AIM is expected to occur at 8.00 a.m. on

Related Party Transaction

Robert W. Duggan is a substantial Shareholder and Glyn Edwards is a director of the Company. Both Mr. Duggan and Mr. Edwards are therefore related parties

pursuant to the AIM Rules. Mr. Duggan s participation in the Subscription and Mr. Edwards participation in the Placing, by way of subscription for 452,475 Placing Shares and receipt of 67,870 Investor Warrants, are deemed to be related

party transactions (the Related Party Transactions ).

The Directors (with the exception of Glyn Edwards), having consulted with Cairn

Financial Advisers LLP, the Company s nominated adviser, consider that the terms of the Related Party Transactions are fair and reasonable insofar as the Shareholders are concerned.

Important Information on Rule 9 Waiver

currently the beneficial owner of approximately 48.78% of the Company s current issued share capital. Mr Duggan has agreed, subject, amongst other things, to the approval of the Resolutions, to subscribe for 166,157,050 Subscription Shares.

This is an amount that would increase his interest in ordinary shares of the Company following completion of the Subscription and the Placing to over 50%, which, without a waiver of the obligations under Rule 9 of the City Code, would oblige Mr

Duggan to make a general offer to Summit Shareholders under Rule 9 of the City Code (a Rule 9 Offer ).

It is expected that Mr Duggan will be

the beneficial owner of approximately 72.78% of the total voting rights of the Company immediately following completion of the Subscription and the Placing.

The Company has applied for a waiver of the requirements for Mr Duggan to make a Rule 9 Offer. The Takeover Panel has agreed to such a waiver, subject to

the passing of a resolution in respect of the Rule 9 Waiver by a poll of independent shareholders at the General Meeting.

Shareholders should be aware that, following completion of the Subscription and the Placing, Mr Duggan will be beneficially interested in more than 50 per cent. of the Company s voting share capital and will be able to increase his

holdings in the Company without incurring an obligation under Rule 9 of the City Code to make a mandatory offer to the other shareholders.

Takeover Panel has confirmed that the Company will remain subject to the Code until such time as both (1) the proposed Board Restructuring has occurred, resulting in the Company s place of central management and control no longer being in the

United Kingdom, Channel Islands and Isle of Man and (2) the Company s shares are no longer admitted to trading on AIM. Subject inter alia to the Cancellation Resolution being approved, it is expected that the Company will no longer be subject

to the Code from 24 February 2020.

For so long as both the Company s place of central management and control is outside the United Kingdom,

Channel Islands and Isle of Man and the Company s shares are not traded on a regulated market or multilateral trading facility in the UK, the Code will not apply to the Company. Therefore in those circumstances Shareholders would not receive

the protections afforded by the Code in the event there is a subsequent offer to acquire their shares in the Company.

Further information on the City

Code and the implications of the AIM Delisting will be available in the Circular.

Importance of the Vote

Unless all of the Resolutions are passed by Shareholders at the General Meeting, the Fundraising will not proceed.

The Company s existing cash and funding arrangements will be sufficient to fund the Company s

operating expenses, including the ongoing Phase 3 clinical trials of ridinilazole for the treatment of C. difficile infection, and capital expenditure requirements through to 31 January 2020. If approved and completed, the Company expects that

the Fundraising will extend this runway by approximately 12 months to 31 January 2021.

If the Fundraising does not proceed, there is no

certainty that the Company will have access to alternative sources of funding, and the Directors would need to consider alternative strategic options that may not be in the best interests of Shareholders including the Company entering into

liquidation or administration. Furthermore, if no alternative sources of funding are available, the Company will be required to reduce its expenditures and stop its ongoing research and development activities including, amongst other things, the

Phase 3 clinical trials of ridinilazole.

The directors therefore believe that the terms of the Fundraising, the proposed Board Restructuring and

the AIM Delisting, are in the best interests of the Company and the Shareholders as a whole.

AIM Rule 17 Schedule 2(g) Disclosure

The following information is disclosed pursuant to AIM Rule 17 and Schedule 2(g) to the AIM Rules for Companies.

a) Mr Robert W. Duggan has held the following directorships and/or partnerships in the past five years:

Mr Duggan s shareholding is disclosed in paragraph 1.1 of Part III of the Circular.

b) Dr Elaine Carla Stracker has held the following directorships and/or partnerships in the past five years:

Dr Stracker does not hold any shares or options in the Company.

c) Mr Manmeet Singh Soni has held the following directorships and/or partnerships in the past five years:

Mr Soni does not hold any shares or options in the Company.

d) Dr Ventzislav Kirilov Stefanov has not held any directorships and/or partnerships in the past five years. Dr Stefanov s shareholding is disclosed in

paragraph 2.1 of Part III of the Circular.

There is no further information to be disclosed in relation to the appointments of Dr Stracker, Mr Soni, Dr

Stefanov or Mr Duggan pursuant to AIM Rule 17 or Schedule Two, paragraph (g) (i)-(viii) of the AIM Rules for Companies.

About Summit Therapeutics

Summit Therapeutics is a leader in antibiotic innovation. Its new mechanism antibiotics are designed to become the new standards of care for the

benefit of patients and create value for payors and healthcare providers. It is currently developing new mechanism antibiotics for infections caused by C. difficile, N. Gonorrhoeae and ESKAPE pathogens and is using its proprietary

Discuva Platform to expand its pipeline. For more information, visit www.Summitplc.com.

For more information, please contact:

This Announcement should be read in its entirety. In particular, you should read and understand the information provided in

the Important Notices section of this Announcement. Shareholders should also read in full the Circular and Form of Proxy being sent to them; the Circular is also being made available online at www.Summitplc.com.

Expected Timetable of Principal Events

Forward Looking Statements

Any statements in this

Announcement about the Company s future expectations, plans and prospects, including but not limited to, whether or not the Company will consummate the Subscription and the Placing and the anticipated use of proceeds from the Subscription and

the Placing, the Board Restructuring, the AIM Delisting, the trading markets for the Company s ordinary shares and ADSs, the clinical and preclinical development of the Company s product candidates, the therapeutic potential of the

Company s product candidates, the potential of the Discuva Platform, the potential commercialisation of the Company s product candidates, the sufficiency of the Company s cash resources, the timing of initiation, completion and

availability of data from clinical trials, the potential submission of applications for marketing approvals and other statements containing the words anticipate, believe, continue, could,

estimate, expect, intend, may, plan, potential, predict, project, should, target, would, and similar expressions,