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Additional Information and Where to Find It

Additional information and where to find it

This communication is being made in respect of the proposed acquisition of Sierra Oncology, Inc. (“Sierra”) by GlaxoSmithKline plc (“GSK”).  In connection with the proposed acquisition, Sierra intends to file with the Securities and Exchange Commission (the “SEC”) and mail to its stockholders a proxy statement (the “Proxy Statement”) in connection with the solicitation of proxies to approve the transaction. Sierra’s stockholders are urged to read the Proxy Statement and any other relevant documents filed with the SEC or delivered to Sierra’s stockholders in connection with the transaction when such materials become available because they will contain important information about the transaction and the parties to the transaction. The Proxy Statement and all other documents filed by or caused to be filed by Sierra with the SEC will be available at no charge on the SEC’s website at You may read and copy those documents or other information filed by Sierra at the SEC public reference room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-0330 for further information on the public reference room. A free copy of the Proxy Statement and all other documents filed by or caused to be filed by Sierra with the SEC will also be available by visiting Sierra’s website (

Participants in the Solicitation

Sierra, GSK, and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from Sierra’s stockholders with respect to the proposed acquisition. Information about Sierra’s directors and executive officers is available in Sierra’s proxy statement dated April 23, 2021 for its 2021 Annual Meeting of Stockholders. Information about GSK’s directors and executive officers can be found in GSK's Annual Report on Form 20-F for 2021. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the Proxy Statement and all other relevant materials to be filed with the SEC or delivered to Sierra’s stockholders regarding the proposed combination when such materials become available. Sierra’s stockholders are urged to read such materials when they become available

Cautionary statement regarding forward-looking statements

GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Such factors include, but are not limited to, those described in GSK's Annual Report on Form 20-F for 2021 and any impacts of the COVID-19 pandemic.

Definitions of Adjusted results, CER growth, CAGR and new GSK are set out on pages 61 and 62 of GSK's fourth quarter 2021 earnings release and pages 56 and 59 of the GSK 2021 Annual Report.  The assumptions and basis for GSK’s Guidance and Outlook are set out on page 69 of the GSK 2021 Annual Report.

This communication includes forward-looking statements related to Sierra, momelotinib and the acquisition of Sierra by GSK, that are subject to risks, uncertainties and other factors. All statements other than statements of historical fact are statements that could be deemed forward-looking statements, including all statements regarding the intent, belief or current expectation of Sierra and members of its senior management team and can typically be identified by words such as “believe,” “expect,” “estimate,” “predict,” “target,” “potential,” “likely,” “continue,” “ongoing,” “could,” “should,” “intend,” “may,” “might,” “plan,” “seek,” “anticipate,” “project” and similar expressions, as well as variations or negatives of these words. Forward-looking statements include, without limitation, statements regarding the business combination, similar transactions, prospective performance, future plans, events, expectations, performance, objectives and opportunities and the outlook for Sierra’s business; the commercial success of Sierra’s products; the anticipated timing of clinical data and regulatory filings or approvals relating to products; the possibility of favourable or unfavourable results from clinical trials; the anticipated benefits of the acquisition; filings and approvals relating to the transaction; the expected timing of the completion of the transaction; the parties’ ability to complete the transaction; and the accuracy of any assumptions underlying any of the foregoing. Investors are cautioned that any such forward-looking statements are not guarantees of future performance and involve risks and uncertainties and are cautioned not to place undue reliance on these forward-looking statements. Actual results may differ materially from those currently anticipated due to a number of risks and uncertainties. Risks and uncertainties that could cause the actual results to differ from expectations contemplated by forward-looking statements include: uncertainties as to the timing of the completion of the merger; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that the required approval of Sierra’s stockholders may not be obtained or that  required regulatory approvals may not be obtained or are obtained subject to conditions that are not anticipated; the occurrence of any event, change or other circumstance that could give rise to the termination of the merger agreement; the failure to realize anticipated benefits of the proposed acquisition when expected or at all; potential adverse reactions or changes to business relationships resulting from the proposed acquisition, including the effect of the announcement on the ability of Sierra to retain and hire key personnel; risks that the proposed acquisition disrupts the current plans and operations of Sierra; transaction costs; risks associated with potential litigation related to the transaction; and other risks and uncertainties described from time to time in documents filed with the SEC by Sierra, including current reports on Form 8-K, quarterly reports on Form 10-Q and annual reports on Form 10-K, as well as the proxy statement to be filed by Sierra, or in GSK’s Annual Report on Form 20-F for 2021 filed with the SEC by GSK. All forward-looking statements are based on information currently available to GSK and Sierra, and neither GSK nor Sierra assumes any obligation to update any forward-looking statements.