This Amendment No. 1 (this “Amendment”) amends and supplements the Tender Offer
Statement on Schedule TO filed with the U.S. Securities and Exchange Commission (the “SEC”) on May 13, 2024 (together with any subsequent amendments and supplements thereto, the “Schedule TO”) by Topaz Merger
Sub, Inc., a Delaware corporation (“Purchaser”) and a wholly owned subsidiary of Ono Pharmaceutical Co., Ltd., a Japanese company (kabushiki kaisha) (“Parent”) and Parent. The Schedule TO relates to the offer
by Purchaser to purchase all of the outstanding shares of common stock, par value $0.01 per share (the “Shares”), of Deciphera Pharmaceuticals, Inc., a Delaware corporation (the “Company”), 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 described in the Offer to Purchase dated May 13, 2024 (as it may be amended
from time to time, the “Offer to Purchase”), and in the related Letter of Transmittal (as it may be amended from time to time, the “Letter of Transmittal” and which, together with the Offer to Purchase, constitutes
the “Offer”), copies of which are attached to and filed with the Schedule TO as Exhibits (a)(1)(i) and (a)(1)(ii), respectively.
Except
as otherwise set forth in this Amendment, the information set forth in the Schedule TO remains unchanged and is incorporated herein by reference to the extent relevant to the items in this Amendment. Capitalized terms used but not defined herein
have the meanings ascribed to them in the Schedule TO.
ITEM 4.
Item 4 of the Schedule TO, to the extent Item 4 incorporates by reference the information contained in the Offer to Purchase, and the information set forth in
Section 17 of the Offer to Purchase titled “Certain Conditions to the Offer” are hereby further amended and supplemented by inserting the following disclosure at the end of such section:
“All Offer Conditions must be satisfied or waived as of the Expiration Date. If we waive a material Offer Condition, we will disseminate
additional tender offer materials and extend the Offer, in each case, if and to the extent required by Rules 14d-4(d)(1), 14d-6(c) and
14e-1 under the Exchange Act.”
ITEMS 1 THROUGH 9; AND ITEM 11.
The information set forth in the Offer to Purchase under Section 18—“Certain Legal Matters; Regulatory Approvals – Antitrust” and
Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items incorporate by reference the information contained in the Offer to Purchase, are hereby amended and supplemented by deleting the second paragraph of the subsection titled
“Antitrust” in the Schedule TO filed with the SEC on May 13, 2024, and adding the following paragraph in its place:
“Under the HSR Act, the purchase of Shares in the Offer may not be completed until the expiration of a 15-calendar-day waiting period following the filing of certain required information and documentary material concerning the Offer (and the Merger) with the FTC and the Antitrust Division, unless the waiting
period is earlier terminated by the FTC and the Antitrust Division. The parties filed such Premerger Notification and Report Forms under the HSR Act with the FTC and the Antitrust Division in connection with the purchase of Shares in the Offer and
the Merger on May 6, 2024. Under the HSR Act, the required waiting period expired at 11:59 p.m., New York City Time on May 21, 2024. Accordingly, the HSR Condition in Section 17—“Certain Conditions to the Offer” has
been satisfied. The Offer continues to be subject to the other Offer Conditions set forth in the Offer to Purchase.”
