This Amendment No. 4 (this “Amendment”) amends and supplements the Tender Offer
Statement on Schedule TO (as amended and together with any amendments and supplements thereto, the “Schedule TO”) filed with the Securities and Exchange Commission on March 18, 2021 by (a) Franklin Acquisition Sub, Inc., a
Delaware corporation (“Purchaser”) and a wholly owned subsidiary of Amgen Inc., a Delaware corporation (“Amgen”), and (b) Amgen. The Schedule TO relates to the offer by Purchaser to purchase all of the
outstanding shares of common stock, par value $0.001 per share (the “Shares”), of Five Prime Therapeutics, Inc., a Delaware corporation (“Five Prime”), at a purchase price of $38.00 per Share, in cash, minus any
applicable withholding taxes and without interest, upon the terms and subject to the conditions set forth in the offer to purchase, dated March 18, 2021, a copy of which is attached as Exhibit (a)(1)(A) (together with any amendments, supplements or
modifications thereto, the “Offer to Purchase”) and in the related Letter of Transmittal (together with any amendments, supplements or modifications thereto, the “Letter of Transmittal” and, together with the Offer
to Purchase, the “Offer”), a copy of which is attached as Exhibit (a)(1)(B).
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 assigned to such terms in the
Offer to Purchase or in the Schedule TO.
The Schedule TO is hereby amended and supplemented as follows:
Items 1 through 9 and Item 11.
The
information set forth in the Offer to Purchase 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, is hereby amended and supplemented to include
the foregoing:
“The Offer and withdrawal rights expired at 12:00 midnight, New York time, on April 16, 2021 (one minute after 11:59 p.m., New
York time, on April 15, 2021). The Depositary has advised Purchaser that a total of 40,392,569 Shares (together with any Shares then owned by Purchaser and its “affiliates” (as such term is defined in Section 251(h)(6)(a) of the
DGCL), but excluding Shares tendered pursuant to guaranteed delivery procedures that have not yet been “received” by the “depository” (as such terms are defined in Section 251(h)(6) of the DGCL)) were validly tendered (and
not properly withdrawn) pursuant to the Offer prior to the Offer Expiration Time, representing approximately 87.8% of the outstanding Shares as of the Offer Expiration Time. In addition, the Depositary has advised Purchaser that Notices of
Guaranteed Delivery have been delivered with respect to 1,039,405 additional Shares prior to the Offer Expiration Time, representing approximately 2.3% of the outstanding Shares as of the Offer Expiration Time.
The number of Shares validly tendered (and not properly withdrawn) pursuant to the Offer (together with any Shares then owned by Purchaser and its
“affiliates” (as such term is defined in Section 251(h)(6)(a) of the DGCL), but excluding Shares tendered pursuant to guaranteed delivery procedures that have not yet been “received” by the “depository” (as such
terms are defined in Section 251(h)(6) of the DGCL)) satisfies the Minimum Condition, and all other conditions to the Offer have been satisfied or (to the extent waivable) waived. Promptly following the Offer Expiration Time, all Shares that
were validly tendered (and not properly withdrawn) pursuant to the Offer were accepted for payment by Purchaser. Purchaser will promptly (but, in any event, within two (2) business days) pay for all such validly tendered Shares in accordance
with the terms of the Offer.