X0306 4 2018-03-09 1 0001412067 Cascadian Therapeutics, Inc. CASC 0001242880 HENNEY CHRISTOPHER S C/O CASCADIAN THERAPEUTICS, INC. 3101 WESTERN AVE., SUITE 600 SEATTLE WA 98121 1 0 0 0 Common Stock 2018-03-09 4 U 0 60185 D 0 D Stock Option (Right to buy) 6.36 2018-03-09 4 D 0 25000 D 2026-03-16 Common Stock 25000 0 D Restricted Stock Units 2018-03-09 4 D 0 13927 D Common stock 13927 0 D Shares of Common Stock tendered in the tender offer launched by Valley Acquisition Sub, Inc. on February 8, 2018 pursuant to that certain Agreement and Plan of Merger, dated January 30, 2018, among Seattle Genetics, Inc., Valley Acquisition Sub, Inc., and Cascadian Therapeutics, Inc. (the "Merger Agreement"), to acquire all of the outstanding shares of common stock of Cascadian Therapeutics, Inc., par value $0.0001 per share, at a purchase price of $10.00 per share ("Offer Price"), net to the seller in cash, without interest and less any required withholding taxes. 25% of the shares subject to the option vest on the first anniversary of the grant date of March 16, 2016, and the remainder vest monthly thereafter for 36 months. All shares subject to this option are fully vested. Pursuant to the Merger Agreement, the option was cancelled in exchange for a cash payment of $91,000.00, which represents the product of (a) the difference between $10.00 and the exercise price of the option per share, multiplied by (b) the number of shares subject to the option. Pursuant to the Merger Agreement, the restricted stock units were cancelled in exchange for a cash payment of $139,270.00, which is the product of the total number of shares subject to such restricted stock unit grant multiplied by the Offer Price. The restricted stock units were granted on June 9, 2017 and vest on the one-year anniversary of the grant date. The restricted stock units expire upon the earlier of the settlement of the units and the unitholder's termination of service. /s/Julia M. Eastland (Attorney-in-Fact) 2018-03-13