X0407 4/A 2023-04-05 2023-04-07 0 0001060736 Seagen Inc. SGEN 0001809717 ROMP CHARLES R 21823 30TH DRIVE SE BOTHELL WA 98021 0 1 0 0 EVP, Commercial U.S. 1 Common Stock 60126 D This amendment to the Form 4 originally filed on April 7, 2023 is being filed solely to check the Rule 10b5-1(c) Transaction Indication box and provide related disclosure. The sale reported on this Form 4 was effected pursuant to a written plan, adopted on May 6, 2020, that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) to satisfy tax obligations arising out of the vesting of previously granted restricted stock units. Amount of securities beneficially owned following reported transactions includes restricted stock units subject to vesting. By: /s/ Jennifer Prosba For: Charles R. Romp 2023-04-12