THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. THIS DOCUMENT INCLUDES A PROPOSAL WHICH, IF IMPLEMENTED, WILL RESULT IN THE DELISTING OF THE AMERICAN DEPOSITARY SHARES, EACH REPRESENTING FIVE ORDINARY S

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION.

THIS DOCUMENT INCLUDES A PROPOSAL WHICH, IF IMPLEMENTED, WILL RESULT IN THE DELISTING OF THE AMERICAN DEPOSITARY SHARES, EACH REPRESENTING FIVE ORDINARY

SHARES IN SUMMIT THERAPEUTICS PLC (INCORPORATED IN ENGLAND AND WALES) (THE OLD SUMMIT ADSs ) FROM THE NASDAQ GLOBAL MARKET AND THE LISTING OF THE SHARES OF COMMON STOCK OF SUMMIT THERAPEUTICS INC. (INCORPORATED IN DELAWARE) (THE NEW

SUMMIT SHARES ) ON THE NASDAQ GLOBAL MARKET.

THIS DOCUMENT IS NOT A PROSPECTUS OR PROSPECTUS EQUIVALENT DOCUMENT.

Part 2 of this document comprises an explanatory statement in compliance with section 897 of the Companies Act 2006. If you are in any doubt as to the

action you should take, you are recommended to seek your own personal financial advice immediately from your stockbroker, bank manager, solicitor, accountant or other independent financial adviser authorised under the Financial Services and Markets

Act 2000 if you are in the United Kingdom, or other appropriately authorised independent financial adviser if you are in a territory outside the United Kingdom.

If you have sold or otherwise transferred all of your Old Summit Shares, please forward this document and the accompanying reply paid envelope (but excluding

any personalised Forms of Proxy) as soon as possible to the purchaser or transferee or to the bank, stockbroker or other agent through whom the sale or transfer was effected, for delivery to the purchaser or transferee. However, such documents

should not be forwarded or transmitted in or into any jurisdiction in which such act would constitute a violation of the relevant laws in such jurisdiction. If you have sold or transferred part of your holding of Old Summit Shares, please consult

the bank, stockbroker or other agent through whom the sale or transfer was effected.

The distribution of this document into jurisdictions other than

the United Kingdom may be restricted by the laws of those jurisdictions and therefore persons into whose possession this document comes should inform themselves about, and observe, any such restrictions. Failure to comply with any such restrictions

may constitute a violation of the securities laws of any such jurisdiction.

Summit Therapeutics plc

(incorporated in England and Wales with registered number 05197494)

Recommended proposals for the introduction of a new US-incorporated

holding company to be effected by means of a Scheme of Arrangement

under Part 26 of the Companies Act 2006

Old Summit Shareholders and/or Old Summit ADS

holders should read carefully the whole of this document, the information incorporated by reference into this document and the accompanying Forms of Proxy. This document is also available on the website of Old Summit at www.summitplc.com.

Your attention is drawn to the letter from the Executive Chairman and Chief Executive Officer of Old Summit in Part 1 of this document which contains the unanimous recommendation of the Old Summit Directors that you vote in favour of the Scheme at

the Court Meeting and the Resolutions to be proposed at the General Meeting. A statement explaining the Scheme in greater detail, which constitutes an explanatory statement in compliance with section 897 of the Companies Act 2006, appears in Part 2

The action to be taken in respect of the Meetings is set out in paragraph 19 of Part 2 of this document. Old Summit Shareholders

will find enclosed with this document a BLUE Form of Proxy for use in connection with the Court Meeting, and a WHITE Form of Proxy for use in connection with the General Meeting.

Please complete and sign both of the enclosed Forms of Proxy in accordance with the instructions printed on

them and return them to Link Asset Services as soon as possible and, in any event, so as to be received at least 48 hours before the time appointed for the relevant Meeting (excluding any part of a day that is not a Business Day). Forms of Proxy

returned by fax will not be accepted.

As an alternative to completing the hard copy Forms of Proxy, you can appoint a proxy electronically by visiting

www.signalshares.com. You will be asked to enter your Investor Code shown on your share certificate and agree to certain terms and conditions. For an electronic proxy appointment to be valid, your appointment must be received by Link Asset

Services not less than 48 hours before the time appointed for holding the relevant Meeting (excluding any part of a day that is not a Business Day).

CREST members who wish to appoint a proxy or proxies by utilising the CREST electronic appointment service, may do so for the Meetings and any adjournment(s)

thereof by utilising the procedures described in the CREST Reference Manual issued by Euroclear UK & Ireland Limited (the CREST Manual ). CREST personal members or other CREST sponsored members and those CREST

members who have appointed (a) voting service provider(s), should refer to their CREST sponsor or voting service provider(s), who will be able to take the appropriate action on their behalf.

In light of the ongoing COVID-19 pandemic and associated difficulties with the holding of physical shareholder

meetings, as permitted by the Corporate Insolvency and Governance Act 2020, the Meetings will be held by telephone. The Company will be providing a listen-only conference call facility to enable Old Summit Shareholders to follow proceedings of the

Meetings remotely. All Old Summit Shareholders are encouraged to use this facility and to follow proceedings of the Meetings in real time if they wish to do so. Any Old Summit Shareholder who wishes to listen to the Meetings by such means should

contact the Company prior to the day of the Meetings via email at investors@summitplc.com (including their Investor Code) in order to request dial-in details. Old Summit Shareholders using the

conference call facility will not be able to vote or ask questions using this service. Accordingly, if Old Summit Shareholders wish to have their vote counted at the Meetings, they must vote by submitting their Forms of Proxy or appointing their

proxy electronically (as the case may be) by the relevant time. The Meetings will end immediately after the formal business. You are therefore strongly urged to return your Forms of Proxy or appoint your proxy electronically (as the case may be),

appointing the chairman of the relevant Meeting as your proxy by the relevant time. Unless the Forms of Proxy are returned by the relevant time, they will be invalid and your vote will not be counted.

If you have any questions relating to this document or the completion and return of the Forms of Proxy, please call Link Asset Services on 0371 664 0321.

Calls are charged at the standard geographic rate and will vary by provider. Calls from outside the United Kingdom will be charged at the applicable international rate. The helpline is open between 9.00 a.m. 5.30 p.m., Monday to Friday

excluding public holidays in England and Wales. Please note that Link Asset Services cannot provide any financial, legal or tax advice and calls may be recorded and monitored for security and training purposes.

Registered holders of Old Summit ADSs as at the ADS Voting Record Time will be contacted by The Bank of New York Mellon as depositary for the Old Summit ADSs

(the Depositary ) with guidelines on how to provide voting instructions to the Depositary with respect to the Old Summit ADSs. In order to vote, holders of Old Summit ADSs are required to follow the voting instructions and to meet

the deadlines provided by the Depositary. Persons that hold Old Summit ADSs in accounts with brokers or other securities intermediaries as at the ADS Voting Record Time should follow the instructions provided by their brokers or other securities

Upon effectiveness of the Scheme, it is expected that the Old Summit ADSs will be delisted and the New Summit Shares will be listed on

the Nasdaq Global Market, and trading in them will commence on the Nasdaq Global Market at the opening of business (New York time) on 21 September 2020.

NO NEW SUMMIT SHARES HAVE BEEN MARKETED TO, NOR ARE ANY NEW SUMMIT SHARES AVAILABLE FOR PURCHASE BY, THE PUBLIC IN THE UNITED KINGDOM OR ELSEWHERE IN

CONNECTION WITH THE INTRODUCTION OF THE NEW SUMMIT SHARES TO THE NASDAQ GLOBAL MARKET.

THIS DOCUMENT DOES NOT CONSTITUTE AN INVITATION OR OFFER TO SELL OR EXCHANGE OR THE SOLICITATION OF AN

INVITATION OR OFFER TO BUY OR EXCHANGE ANY SECURITY OR TO BECOME A STOCKHOLDER OF NEW SUMMIT. NONE OF THE SECURITIES REFERRED TO IN THIS DOCUMENT SHALL BE SOLD, ISSUED, EXCHANGED OR TRANSFERRED IN ANY JURISDICTION IN CONTRAVENTION OF APPLICABLE

OVERSEAS SHAREHOLDERS

publication or distribution of this document in certain jurisdictions may be restricted by law. Persons who are not resident in the United Kingdom or who are subject to the laws and/or regulations of another jurisdiction should inform themselves of,

and should observe, any applicable requirements. Any failure to comply with these requirements may constitute a violation of the securities laws of any such jurisdiction. To the fullest extent permitted by applicable law, the companies and persons

involved in the Proposals disclaim any responsibility or liability for the violation of such requirements by any person.

Unless otherwise permitted by

applicable law and regulation, this document (and the matters referred to herein) will not be made available, directly or indirectly, in, into or from a jurisdiction where to do so would violate the laws in that jurisdiction, and no person may vote

in favour of the Proposals by any such use, means, instrumentality or form within any jurisdiction if to do so would constitute a violation of the laws of that jurisdiction. Accordingly, copies of this document and all documents relating to the

Proposals are not being, and must not be, directly or indirectly, mailed or otherwise forwarded, distributed or sent in, into or from a jurisdiction where to do so would violate the laws in that jurisdiction, and persons receiving this document and

all documents relating to the Proposals (including custodians, nominees and trustees) must not mail or otherwise distribute or send them in, into or from such jurisdictions where to do so would violate the laws in that jurisdiction. Any person

(including, without limitation, any custodian, nominee and trustee) who would, or otherwise intends to, or who may have a contractual or legal obligation to, forward this document and/or any other related document to any jurisdiction outside the UK

should inform themselves of, and observe, any applicable legal or regulatory requirements of their jurisdiction.

The availability of this document to Old

Summit Shareholders and/or Old Summit ADS holders who are not resident in the United Kingdom may be affected by the laws of the relevant jurisdictions in which they are resident (including affecting the ability of such Old Summit Shareholders to

vote their Old Summit Shares and/or Old Summit ADS holders to vote their Old Summit ADSs with respect to the Scheme and the Proposals at the Meetings, or to execute and deliver Forms of Proxy appointing another to vote at the Meetings on their

behalf). Persons who are not resident in the United Kingdom or who are subject to the laws and/or regulations of another jurisdiction should inform themselves of, and should observe, any applicable requirements.

Overseas Shareholders should consult their own legal and tax advisers with respect to the legal and tax consequences of the Scheme in their particular

INFORMATION FOR UNITED STATES SHAREHOLDERS

The cancellation of the Scheme Shares and the allotment and issue of the New Summit Shares relate to shares of a UK company and a US company respectively and

are proposed to be effected by means of a scheme of arrangement under the laws of England and Wales. A transaction effected by means of a scheme of arrangement is not subject to proxy solicitation or tender offer rules under the US Securities

Exchange Act of 1934, as amended (the US Exchange Act ). Accordingly, the Scheme is subject to the disclosure requirements, rules and practices applicable in the United Kingdom to schemes of arrangement, which differ from the

requirements of US proxy solicitation or tender offer rules under the US Exchange Act.

The New Summit Shares will not be registered under the US

Securities Act of 1933, as amended (the US Securities Act ), or under the securities laws of any state or other jurisdiction of the United States. Accordingly, the New Summit Shares may not be offered, sold, resold, delivered,

distributed or otherwise transferred, directly or indirectly, in or into the United States absent registration under the US Securities Act or pursuant to an exemption therefrom. The New Summit Shares are expected to be issued in reliance upon the

exemption from the registration requirements of the US Securities Act provided by Section 3(a)(10) thereof. Shareholders who are affiliates of New Summit after the Scheme becomes Effective will be subject to certain US transfer restrictions

relating to the New Summit Shares received in connection with the Scheme. Shareholders who are not affiliates of New Summit after the Scheme becomes Effective may resell their New Summit Shares without restriction under the US Securities Act.

For the purposes of qualifying for the exemption from the registration requirements of the US Securities Act

afforded by Section 3(a)(10), Old Summit will advise the Court through counsel that its sanctioning of the Scheme will be relied upon by New Summit as an approval of the Scheme following a hearing on its fairness to Old Summit Shareholders at

which hearing all such Old Summit Shareholders will be entitled to attend themselves or through counsel to support or oppose the sanctioning of the Scheme and with respect to which notification has been or will be given to all such Old Summit

Shareholders. In light of the ongoing COVID-19 pandemic, the Court Hearing is likely to be conducted via Skype. If you are interested in attending the Court Hearing via Skype, you are directed to the Business

and Property Courts Rolls Building Cause List at justice.gov.uk for details of how to do so. The time of the Court Hearing and information on how to attend will be updated on the Court s website after 4.30 p.m. on the Business Day before the

It may be difficult for US Shareholders and US holders of Old Summit ADSs to enforce their rights and claims arising out of the US federal

securities laws, since Old Summit is located in a country other than the United States. US Shareholders may not be able to sue a non-US company or its officers or directors in a

non-US court for violations of the US securities laws. Further, it may be difficult to compel a non-US company and its affiliates to subject themselves to a US

None of the securities referred to in this document has been approved or disapproved by the SEC, any state securities commission

in the United States or any other US regulatory authority, nor have such authorities passed upon or determined the adequacy or accuracy of the information contained in this document. Any representation to the contrary is a criminal offence in the

US Shareholders and US holders of Old Summit ADSs should note that no appraisal or similar rights of dissenting shareholders are to apply

in connection with the Scheme as none are required as a matter of English law.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This document contains statements about Old Summit and New Summit that are or may be forward-looking statements. All statements other than statements of

historical facts included in this document may be forward-looking statements. Without limitation, any statements preceded or followed by or that include the words targets , plans , believes , expects ,

aims , intends , will , may , anticipates , estimates , projects or words or terms of similar substance or the negative thereof, are forward-looking statements.

Forward-looking statements include statements relating to the following: (i) expectations with respect to the timetable for completing the Scheme; (ii) potential benefits of the Scheme; (iii) future capital expenditures, expenses,

revenues, earnings, synergies, economic performance, indebtedness, financial condition, dividend policy, losses and future prospects; (iv) business and management strategies and the expansion and growth of Old Summit or New Summit s

operations; and (v) the effects of Government regulation on Old Summit or New Summit s business.

Such forward-looking statements involve risks