X0306 4 2022-05-13 0 0001060736 Seagen Inc. SGEN 0001263508 BAKER BROS. ADVISORS LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 0001363364 Baker Brothers Life Sciences LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 0001551139 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 0001087939 BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 0001087940 BAKER FELIX 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 0001580575 Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET, 3RD FLOOR NEW YORK NY 10014 1 0 1 0 Common Stock 23280 D Common Stock 23277 D Common Stock 2022-05-13 4 A 0 1503 0.00 A 4088765 I See footnotes Common Stock 2022-05-13 4 A 0 1503 0.00 A 42966507 I See footnotes Non-Qualified Stock Option (right to buy) 135.63 2022-05-13 4 A 0 3676 0.00 A 2023-05-13 2032-05-13 Common Stock 3676 3676 I See footnotes Reflects shares of common stock ("Common Stock") of Seagen Inc. (the "Issuer") held directly by Felix J. Baker. Reflects Common Stock held directly by Julian C. Baker. After giving effect to the transaction reported herein and as a result of their ownership interest in (i) Baker Biotech Capital, L.P. and (ii) 667, L.P. ("667"), Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in Common Stock reported in column 5 of Table I directly held by 667, a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP),LLC, due to their interest in 667 and Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667. Restricted stock units (each an "RSU") payable solely in Common Stock of the Issuer granted to Felix J. Baker on May 13, 2022, pursuant to the Amended and Restated 2007 Equity Incentive Plan of the Issuer. The RSUs fully vest on May 13, 2023. Baker Bros. Advisors LP (the "Adviser") serves as the investment adviser to 667 and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds"). In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held by the Funds. Baker Bros. Advisors (GP) LLC (the "Adviser GP") is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are managing members of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held by the Funds. The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is a beneficial owner of such securities for purposes of Section 16 or any other purpose. Pursuant to agreements between Felix J. Baker and the Adviser, the Adviser has voting and dispositive power over non-qualified options exercisable into Common Stock of the Issuer ("Stock Options"), RSUs and any Common Stock received as a result of the exercise of Stock Options or vesting of RSUs. Pursuant to the policies of the Adviser, Felix J. Baker does not have a right to any of the Issuer's securities issued in lieu of director retainer fees and the Funds are entitled to an indirect proportionate pecuniary interest in the securities. The Funds each own an indirect proportionate pecuniary interest in the shares of Common Stock. Solely as a result of their ownership interest in (i) the general partners of the Funds and (ii) the Funds, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in the shares of Common Stock issued in lieu of director retainer fees, Stock Options, Common Stock issued upon exercise of Stock Options, RSUs and Common Stock received upon vesting of RSUs (ie. no direct pecuniary interest). The disclosure of the grant of RSUs reported on this form is a single grant of 1,503 RSUs. The grant of 1,503 RSUs is reported for each of the Funds as each has an indirect pecuniary interest in such securities. Includes beneficial ownership of 27,500 previously issued RSUs payable solely in Common Stock issued to Felix Baker in his capacity as a director of the Issuer pursuant to the Amended and Restated 2007 Equity Incentive Plan of which the Funds may be deemed to own a portion and 112,500 previously issued shares from exercise of 112,500 Stock Options of the Issuer that were issued to Felix J. Baker in his capacity as a director of the Issuer, of which the Funds may be deemed to own a portion. The policy of the Funds and the Adviser does not permit full-time employees of the Adviser or managing members of the Adviser GP to receive compensation for serving as a director of the Issuer. After giving effect to the transaction reported herein and as a result of their ownership interest in (i) Baker Brothers Life Sciences Capital, L.P. and (ii) Life Sciences, Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in Common Stock reported in column 5 of Table I directly held by Life Sciences, a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to their interest in Life Sciences and Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences. Stock Options granted to Felix J. Baker on May 13, 2022, pursuant to the Issuer's Amended and Restated 2007 Equity Incentive Plan. The Stock Options with a strike price of $135.63 vest on May 13, 2023 and expire on May 13, 2032. Felix J. Baker is a director of Seattle Genetics, Inc. (the "Issuer"). By virtue of their representation on the Board of Directors of the Issuer, for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the reporting persons are deemed directors by deputization of the Issuer. By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2022-05-17 Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to BAKER BROTHERS LIFE SCIENCES, L.P., pursuant to authority granted by Baker Brothers Life Sciences Capital, L.P., GP to Baker Brothers Life Sciences, L.P., Name: Scott L. Lessing, Title: President /s/ 2022-05-17 Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to 667, L.P., pursuant to authority granted by Baker Biotech Capital, L.P., GP to 667, L.P. Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2022-05-17 Julian C. Baker 2022-05-17 Felix J. Baker 2022-05-17 By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2022-05-17