UNITED STATES SECURITIES AND EXCHANGE COMMISSION Table of Contents Washington, D.C. 20549 Form 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2021 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number: 0-32405 SEAGEN INC. (Exact name of registrant as specified in its charter) (State or other Jurisdiction of incorporati ...