13D Filing: Lansdowne Partners and Summit Therapeutics PLC (ADR) (SMMT)

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Schedule 13D/A

Amendment No. 3

INFORMATION TO BE INCLUDED IN STATEMENTS
FILED PURSUANT TO RULES 13d-1 (a) AND

AMENDMENTS THERETO FILED PURSUANT TO
13d-2 (a)

If the filing
person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D/A, and
is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box o.

Note: Schedules
filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for
other parties to whom copies are to be sent.

* The remainder
of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of
securities and for any subsequent amendment containing information which would alter disclosures provided in the cover page.

The information
required on the remainder of this cover page shall not be deemed to be “filed” for the purposes of Section 18 of the
Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall
be subject to all other provisions of the Act (however, see the Notes).

_________________

⁽¹⁾ The 19,060,500 Ordinary Shares beneficially owned
consist of 11,077,170 Ordinary Shares and 1,596,666 American Depositary Shares, which may be exchanged for Ordinary Shares at a
1:5 ratio.

__________________

⁽²⁾ The 19,060,500 Ordinary Shares beneficially owned
consist of 11,077,170 Ordinary Shares and 1,596,666 American Depositary Shares, which may be exchanged for Ordinary Shares at a
1:5 ratio.

Statement on Schedule 13D/A

This statement on
Schedule 13D/A (the “Schedule 13D/A“) relates to the Ordinary Shares, par value £0.01 per share (the “Ordinary
Shares“) and the American Depositary Shares, each representing five Ordinary Shares (the “ADSs” and
together with the Ordinary Shares, the “Shares”), of Summit Therapeutics PLC, a foreign private issuer incorporated
in England and Wales whose principal executive office is located at 136A Eastern Avenue, Milton Park, Abingdon, Oxfordshire OX14
4SB, United Kingdom (the “Issuer“).

(a-c, f) This
Schedule 13D/A is being filed on behalf of: (i) Lansdowne Partners (UK) LLP, an English limited liability partnership (“Lansdowne“)
and (ii) Lansdowne Developed Markets Master Fund Limited, a Cayman Islands exempted company (the “Fund” and together
with Lansdowne, the “Reporting Persons”). The Fund is a privately offered investment fund that holds the Shares
reported in this Schedule 13D/A. Lansdowne is the investment adviser to the Fund and as a result is the beneficial owner of the
Shares reported in this Schedule 13D/A.

The principal business address of Lansdowne
is 15 Davies Street, London W1K 3AG, England and the principal business address of the Fund is c/o BNP Paribas Fund Administration
Services, 2 Grand Canal Plaza, Grand Canal Street, Dublin 2, Ireland.

(d)       None
of the Reporting Persons, individually or collectively, has, during the last five years, been convicted in a criminal proceeding
(excluding traffic violations or similar misdemeanors).

(e)       None
of the Reporting Persons has, during the last five years, been a party to a civil proceeding of a judicial or administrative body
of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future
violations of, or prohibiting or mandating activities subject to, Federal or state securities laws or finding any violation with
respect to such laws.

The funds for the
purchase of the Shares beneficially owned by the Reporting Persons came from the working capital of the Fund. The total cost for
the Ordinary Shares beneficially owned by the Reporting Persons is £18,676,103 and the total cost for the ADSs beneficially
owned by the Reporting Persons is $17,373,659. No borrowed funds were used to purchase the Shares, other than any borrowed funds
used for working capital purposes (including certain leverage arrangements) in the ordinary course of business.

The Reporting Persons
hold the securities described in Item 5 of this statement for investment purposes only.

The Reporting Persons
have no plan or proposal which relates to, or would result in, any of the actions enumerated in Item 4 of the instructions to Schedule
13D/A.

(a – e) Regarding
aggregate beneficial ownership, see Row 11 of the cover page of each Reporting Person. Regarding percentage beneficial ownership,
see Row 13 of the cover page of each Reporting Person. Regarding sole power to vote shares, see Row 7 of the cover page of each
Reporting Person. Regarding shared power to vote shares, see Row 8 of the cover page of each Reporting Person. Regarding sole power
to dispose of shares, see Row 9 of the cover page of each Reporting Person. Regarding shared power to dispose of shares, see Row
10 of the cover page of each Reporting Person.

There have been
no transactions by the Reporting Persons in the Shares during the past sixty days.

None

SIGNATURES

After reasonable
inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete
and correct.

Date: January 30, 2018

Exhibit A

AGREEMENT

The undersigned agree that this Schedule
13D/A, dated January 30, 2018, relating to the Ordinary Shares, par value £0.01 per share and the American Depositary
Shares, each representing five Ordinary Shares, of Summit Therapeutics PLC shall be filed on behalf of the undersigned.

Date: January 30, 2018