UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16 OF

THE SECURITIES EXCHANGE ACT OF 1934

For the month of March, 2015

Commission File Number 001-36866

SUMMIT THERAPEUTICS PLC

(Translation of registrant’s name into English)

85b Park Drive

Milton Park, Abingdon

Oxfordshire OX14 4RY

United Kingdom

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

FORM 20-F  x            FORM 40-F  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ¨

Indicate by check mark whether the registrant by furnishing the information contained in this form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934:

YES  ¨            NO   x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-             

Exercise of Over-Allotment Option

On March 18, 2015, Summit Therapeutics plc issued a press release in the United States announcing that the underwriters of its recently closed initial public offering on the NASDAQ Global Market have exercised in full their over-allotment option to purchase an additional 517,500 American Depositary Shares.

The press release is attached to this report on Form 6-K as Exhibit 99.1.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

	SUMMIT THERAPEUTICS PLC
By:	/s/ Erik Ostrowski
	Erik Ostrowski
	Chief Financial Officer

Date: March 19, 2015

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EXHIBIT INDEX

Exhibit Number	Description
99.1	Press Release dated March 18, 2015

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