This Amendment No. 2 (this Amendment) amends and supplements the
Solicitation/Recommendation Statement on Schedule 14D-9 (as amended or supplemented from time to time, the Schedule 14D-9) filed by Deciphera
Pharmaceuticals, Inc., a Delaware corporation (Deciphera), with the Securities and Exchange Commission (the SEC) on May 13, 2024, relating to the tender offer by Topaz Merger Sub, Inc., a Delaware corporation
(Merger Sub) and a wholly owned subsidiary of ONO Pharmaceutical Co., Ltd., a Japanese company (kabushiki kaisha) (ONO), to acquire all of the issued and outstanding shares of common
stock, par value $0.01 per share, of Deciphera (the Shares) at a price per Share of $25.60, net to the seller in cash, without interest and subject to any withholding of taxes required by applicable law, upon the terms and subject to the
conditions set forth in the Offer to Purchase, dated May 13, 2024 (as amended or supplemented from time to time, the Offer to Purchase), and in the related Letter of Transmittal, each as filed by ONO and Merger Sub with the SEC on
May 13, 2024 (as amended or supplemented from time to time, the Letter of Transmittal, which, together with the Offer to Purchase, constitute the Offer).
On May 21, 2024, a complaint was filed by a purported Deciphera stockholder in connection with the proposed Offer and Merger, captioned Zalvin v.
Deciphera Pharmaceuticals, Inc., et al., No. 2481CV01338 (Mass. Sup. Ct., Middlesex Cty.) (the Merger Action). The Merger Action generally alleges that the Schedule 14D-9 misrepresents
and/or omits certain purportedly material information relating to the Merger and seeks, among other relief, an injunction enjoining the Merger unless and until certain additional information is disclosed to Deciphera stockholders, costs of the
action, including plaintiffs attorneys fees and experts fees, and other relief the court may deem just and proper. The Merger Action asserts claims for negligence and negligent misrepresentation against the Board of Directors of
Deciphera, Deciphera, and ONO.
Deciphera believes that no supplemental disclosure is required under applicable laws and that the Schedule 14D-9 disclosed all material information required to be disclosed therein. However, to avoid the risk that the Merger Action may delay or otherwise adversely affect the Merger and to
minimize the expense of defending the Merger Action, Deciphera wishes to make voluntarily certain supplemental disclosures related to the proposed Merger, all of which are set forth below and should be read in conjunction with the Schedule 14D-9. Nothing in these supplemental disclosures shall be deemed an admission of the legal necessity or materiality under applicable laws of any of the disclosures set forth herein.