THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are in any doubt about the contents of this Document or what action you should take, you should immediately consult your stockbroker, bank manager,

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are in any doubt about the contents of this Document or what action you should

take, you should immediately consult your stockbroker, bank manager, solicitor or other independent financial adviser authorised under FSMA if you are in the United Kingdom or, if not, another appropriately authorised independent financial adviser.

You should be aware that an investment in the Company involves a high degree of risk and prospective investors should in particular carefully consider the section entitled Risk Factors set out in Part II of this Document.

If you have sold or otherwise transferred, or you sell or otherwise transfer, all of your holding of ordinary shares in Summit Therapeutics PLC please send

this Document together with the accompanying Form of Proxy at once to the purchaser or transferee or to the stockbroker, bank or other agent through or by whom the sale or transfer was or is effected, for onward delivery to the purchaser or

The whole of this Document should be read. Your attention is drawn to the letter from the Chairman of the Company, which is set out in

Part I of this Document and which recommends that, to the extent you are entitled to do so, you vote in favour of the Resolutions to be proposed at the General Meeting.

Neither the Placing nor the Subscription constitutes an offer of transferable securities to the public (within the meaning of section 102B of FSMA) requiring

an approved prospectus under section 85 of FSMA and accordingly this Document does not constitute a prospectus for the purpose of the Prospectus Rules of the UK Financial Conduct Authority or an admission document for the purpose of the AIM Rules.

Accordingly, this Document has not been, and will not be, reviewed or approved by the UK Financial Conduct Authority pursuant to sections 85 and 87 of FSMA, the London Stock Exchange or any other authority or regulatory body and has not been

approved for the purposes of Section 21 of FSMA. In addition, this Document does not constitute an admission document drawn up in accordance with the AIM Rules and this Document shall not constitute an offer to sell or a solicitation of an

offer to buy any securities, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful.

Summit Therapeutics PLC

(Incorporated and registered in England and Wales under number 05197494)

Proposed Fundraising comprising a Subscription and a Placing of 175,378,450 New Ordinary Shares in aggregate at a price of 22.1 pence per

New Ordinary Share and Issue of Investor Warrants

Approval of a waiver of obligations under Rule 9 of the Takeover Code

Cancellation of trading on AIM

Copies of this Document are available free of charge during normal business hours on any weekday (except Saturdays, Sundays and public holidays) from Summit

Therapeutics PLC s registered office from the date of this Document to the date of admission of the New Ordinary Shares.

Application will be made

for the New Ordinary Shares to be admitted to trading on the AIM market of the London Stock Exchange. Subject to certain conditions being satisfied, including the passing of the Resolutions at the General Meeting, it is expected that admission to

trading on AIM and dealings in the New Ordinary Shares will commence on or around 30 December 2019.

AIM is a market designed for emerging or smaller companies to which a higher investment risk tends to be

attached than to larger or more established companies. AIM securities are not admitted to the Official List of the United Kingdom Listing Authority. A prospective investor should be aware of the risks of investing in such companies and should make

the decision to invest only after careful consideration, and if appropriate, consultation with a financial adviser.

Cairn Financial Advisers LLP is

authorised and regulated by the UK Financial Conduct Authority and is acting exclusively for the Company as financial adviser and adviser pursuant to rule 3 of the Code in connection with the Fundraising and the Rule 9 Waiver respectively and for no

one else and will not be responsible to anyone other than the Company for providing the protections afforded to its customers or for affording advice in relation to the matters referred herein. Cairn Financial Advisers LLP does not accept any

liability whatsoever for the accuracy or opinions contained in this Document (or for omission of any material information) and shall not be responsible for the contents of this Document.

Nplus1 Singer Advisory LLP is authorised and regulated by the UK Financial Conduct Authority and is acting for the Company as a Broker and for no one else in

connection with the Fundraising and will not be responsible to anyone other than the Company for providing the protections afforded to its customers or for affording advice in relation to the matters referred herein. N+1 Singer does not accept any

liability whatsoever for the accuracy or opinions contained in this Document (or for omission of any material information) and shall not be responsible for the contents of this Document. No person should construe the contents of this Document as

legal, tax or financial advice and recipients of this Document should consult their own advisers as to the matters described in this Document. The contents of the Company s website or any website directly or indirectly linked to the

Company s website do not form part of this Document.

Notice of a General Meeting of Summit Therapeutics PLC 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 is set out at the end of this Document. Shareholders will find enclosed with this Document a Form of Proxy for use at the General

Meeting. If you do not intend on being present at the General Meeting, please complete the Form of Proxy in accordance with the instructions thereon and return it as soon as possible but, in any event, so as to be received by Link Asset Services,

PXS, 34 Beckenham Road, Beckenham, Kent BR3 4TU at least 48 hours before the time appointed for the General Meeting.

None of the New Ordinary Shares, the

Investor Warrants, the Form of Proxy, this Document or any other document connected with the Fundraising have been or will be approved or disapproved by the US Securities and Exchange Commission or by the securities commissions of any state or other

jurisdiction of the United States or any other regulatory authority, nor have any of the foregoing authorities or any securities commission passed comment upon or endorsed the merits of the offering of the New Ordinary Shares and the Investor

Warrants, the Form of Proxy, or the accuracy or adequacy of this Document or any other document connected with the Fundraising. Any representation to the contrary is a criminal offence. The distribution of this Document and the Form of Proxy in

jurisdictions other than the UK may be restricted by law and therefore persons into whose possession this Document and/or the Form of Proxy come should inform themselves about and observe any such restrictions. Any failure to comply with any such

restrictions may constitute a violation of the securities laws or regulations of such jurisdictions.

The New Ordinary Shares and the Investor Warrants

have not been registered under the US Securities Act 1933 (as amended) (the Securities Act ) or under the applicable securities laws of any state or other jurisdiction of the United States or any of the other Restricted

Jurisdictions (such jurisdictions being the United States, Australia, Canada, Japan, New Zealand and South Africa and any other jurisdiction where the extension or availability of the Fundraising would breach any applicable law). The New

Ordinary Shares and the Investor Warrants may not be offered, sold, taken up, resold, transferred or delivered, directly or indirectly, within, into or in the United States, or any Restricted Jurisdiction or to any national resident or citizen of,

or any corporation, partnership or other entity created or organised under the laws of any Restricted Jurisdiction, except pursuant to an applicable exemption from, or in a transaction not subject to, the registration requirements of the Securities

Act and in compliance with the securities laws of any relevant state or other jurisdiction of the United States and any relevant Restricted Jurisdiction. The Subscription Shares and the related Investor Warrants are being offered and sold to an

accredited investor pursuant to an exemption from registration under Regulation D of the Securities Act, and the Placing Shares and the related Investor Warrants are being offered and sold outside of the United States in offshore transactions

pursuant to Regulation S of the Securities Act. The Placing Shares and the related Investor Warrants may not be offered or sold, directly or indirectly, in or into the United States or to, or for the account or benefit of, a U.S. Person (as defined

in Regulation S of the Securities Act), except pursuant to an applicable exemption from, or in a transaction not subject to, the registration requirements of the Securities Act. There will be no public offering of the New Ordinary Shares or the

Investor Warrants in the United States.

Notice to overseas persons

None of the New Ordinary Shares or the Investor Warrants have been registered under the Securities Act or under the securities legislation of any state or

other jurisdiction of the United States. The distribution of this Document in certain jurisdictions other than the United Kingdom may be restricted by law and therefore persons into whose possession this Document comes should inform themselves about

and observe any such restrictions. Any failure to comply with these restrictions may constitute a violation of the securities laws of any such jurisdiction.

It is the responsibility of any person receiving a copy of this Document outside the United Kingdom to satisfy himself as to the full observance of the laws

and regulatory requirements of the relevant territory in connection therewith, including obtaining any governmental or other consents which may be required or observing any other formalities required to be observed in such territory and paying any

other issue, transfer or other taxes due in such other territory.

Cautionary note regarding forward-looking statements

This Document contains certain statements about Summit Therapeutics PLC and certain of its current plans, goals and expectations relating to its future

financial condition and performance and which involve a number of risks and uncertainties. The Company cautions readers that no forward-looking statements are a guarantee of future performance and that actual results could differ materially from

those contained in such forward-looking statements. All statements, other than statements of historical facts, included in this Document including statements about the completion of the proposed sale of New Ordinary Shares and the Investor Warrants,

development and potential commercialisation of Summit Therapeutics PLC product candidates, the therapeutic potential of Summit Therapeutics PLC preclinical and clinical product candidates, the timing of initiation, completion and availability of

data from clinical trials, the potential of the Discuva Platform, the potential benefits and future operation of the collaboration with Eurofarma Laborat rios SA, the awards from BARDA and CARB-X,

including any potential future payments thereunder, any other potential third-party collaborations and expectations regarding the sufficiency of our cash balance and any proceeds from the sale of the New Ordinary Shares and the Investor Warrants to

fund operating expenses and capital expenditures, and other statements preceded or followed by, or that include, the words targets , plans , believes ,

expects , aims , intends , will , may , should , anticipates ,

estimates , projects or words or terms of similar substance or the negative thereof, are or may be forward-looking statements. Forward-looking statements also include statements relating to the

following: (i) future capital expenditures, expenses, revenues, earnings, synergies, economic performance, indebtedness, financial condition, dividend policy, losses and future prospects and (ii) business and management strategies and the

expansion and growth of the operations of Summit Therapeutics PLC. These forward-looking statements are not guarantees of future performance and have not been reviewed by the auditors of Summit Therapeutics PLC. By their nature, forward-looking

statements involve known and unknown risks, uncertainties and other factors (a number of which are beyond the Company s control) which may cause the actual results, performance or achievements of any such person, or industry results, to be

materially different from any results, performance or achievements expressed or implied by such forward-looking statements. (These factors are discussed in the Risk Factors section of filings that Summit Therapeutics PLC makes with the

Securities and Exchange Commission, including its Annual Report on Form 20-F for the fiscal year ended 31 January 2019.) These forward-looking statements are based on assumptions regarding the present and

future business strategies of Summit Therapeutics PLC and the environment in which it will operate in the future. Investors should not place undue reliance on such forward-looking statements and, save as is required by law or regulation (including

to meet the requirements of the AIM Rules, the Disclosure Guidance and Transparency Rules and/or the Prospectus Rules), Summit Therapeutics PLC does not undertake any obligation to update publicly or revise any forward-looking statements (including

to reflect any change in expectations with regard thereto or any change in events, conditions or circumstances on which any such statement is based). All subsequent oral or written forward-looking statements attributed to Summit Therapeutics PLC or

any persons acting on its behalf are expressly qualified in their entirety by the cautionary statement above. All forward-looking statements contained in this Document are based on information available to the Directors of Summit Therapeutics PLC at

the date of this Document, unless some other time is specified in relation to them, and the posting or receipt of this Document shall not give rise to any implication that there has been no change in the facts set forth herein since such date.

DIRECTORS, SECRETARY AND ADVISERS

EXPECTED TIMETABLE OF PRINCIPAL EVENTS

FUNDRAISING STATISTICS

LETTER FROM THE CHAIRMAN OF SUMMIT THERAPEUTICS PLC

(Incorporated and registered in England and Wales with registered no. 05197494)

To all Shareholders and to the holders of ADSs and, for information, to holders of options over Ordinary Shares

Proposed Fundraising comprising a Subscription and Placing of 175,378,450 New Ordinary Shares at a price of 22.1 pence per New Ordinary

Issue of Investor Warrants