X0306 4 2018-03-09 1 0001412067 Cascadian Therapeutics, Inc. CASC 0001644965 Growth Equity Opportunities IV, LLC 1954 GREENSPRING DRIVE, SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001629794 New Enterprise Associates 15, L.P. 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001640031 NEA Partners 15, L.P. 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 0001640033 NEA 15 GP, LLC 1954 GREENSPRING DRIVE SUITE 600 TIMONIUM MD 21093 0 0 1 0 Common Stock 2018-03-09 4 U 0 10882574 D 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., to acquire all of the outstanding shares of common stock of Cascadian Therapeutics, Inc., par value $0.001 per share, at a purchase price of $10.00 per share, net to the seller in cash, without interest and less any required withholding taxes. The shares are directly held by Growth Equity Opportunities Fund IV, LLC ("GEO IV") and indirectly held by New Enterprise Associates 15, L.P. ("NEA 15"), the sole member of GEO IV, NEA Partners 15, L.P. ("NEA Partners 15"), the sole general partner of NEA 15, NEA 15 GP, LLC ("NEA 15 GP"), the sole general partner of NEA Partners 15, and the individual managers of NEA 15 GP (NEA 15, NEA Partners 15, NEA 15 GP and the individual managers of NEA 15 GP, together, the "Indirect Reporting Persons").The individual managers of NEA 15 GP are Peter J. Barris, Forest Baskett, Anthony A. Florence, Jr., Josh Makower, David M. Mott, Jon Sakoda, Scott D. Sandell, Peter W. Sonsini and Ravi Viswanathan. The Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the shares of the Issuer held by GEO IV in which the Indirect Reporting Persons have no pecuniary interest. /s/ Sasha Keough, attorney-in-fact 2018-03-13