X0306 4 2020-05-06 0 0001060736 SEATTLE GENETICS INC /WA SGEN 0001263508 BAKER BROS. ADVISORS 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 0001580575 Baker Bros. Advisors (GP) LLC 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 0001087940 BAKER FELIX 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 Common Stock 181740 D Common Stock 181733 D Common Stock 2020-05-06 4 S 0 4204 164.0597 D 4315650 I See footnotes Common Stock 2020-05-06 4 S 0 45606 164.0597 D 45814543 I See footnotes Common Stock 2020-05-06 4 S 0 16485 164.5964 D 4299165 I See footnotes Common Stock 2020-05-06 4 S 0 178862 164.5964 D 45635681 I See footnotes Common Stock 2020-05-06 4 S 0 8444 165.7040 D 4290721 I See footnotes Common Stock 2020-05-06 4 S 0 91613 165.7040 D 45544068 I See footnotes Common Stock 2020-05-06 4 S 0 3786 166.6236 D 4286935 I See footnotes Common Stock 2020-05-06 4 S 0 41072 166.6236 D 45502996 I See footnotes Common Stock 2020-05-07 4 S 0 1489 163.4142 D 4285446 I See footnotes Common Stock 2020-05-07 4 S 0 16159 163.4142 D 45486837 I See footnotes Common Stock 2020-05-07 4 S 0 7805 164.1940 D 4277641 I See footnotes Common Stock 2020-05-07 4 S 0 84663 164.1940 D 45402174 I See footnotes Common Stock 2020-05-07 4 S 0 4505 164.9574 D 4273136 I See footnotes Common Stock 2020-05-07 4 S 0 48880 164.9574 D 45353294 I See footnotes Common Stock 2020-05-07 4 S 0 400 166.1547 D 4272736 I See footnotes Common Stock 2020-05-07 4 S 0 4343 166.1547 D 45348951 I See footnotes Common Stock 2020-05-08 4 S 0 42197 158.5000 D 4230539 I See footnotes Common Stock 2020-05-08 4 S 0 457803 158.5000 D 44891148 I See footnotes Reflects shares of common stock ("Common Stock") of Seattle Genetics, Inc. (the "Issuer") held directly by Felix J. Baker. Reflects Common Stock held directly by Julian C. Baker. The price reported in Column 4 is a weighted average price. These shares were traded by 667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds") in multiple transactions at prices ranging from $163.74 to $164.17, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission (the "Staff"), upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. 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, 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. Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to 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. Solely as a result of their ownership interest in (i) the general partners of the Funds and (ii) the Funds as limited partners, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in the Common Stock issued upon exercise of stock options ("Stock Options") and Common Stock received upon vesting of restricted stock units. (i.e. no direct pecuniary interest) 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. Includes beneficial ownership of 24,763 previously issued restricted stock units 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 77,500 previously issued shares from exercise of 77,500 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. 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. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $164.23 to $165.20, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $165.21 to $166.205, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $166.25 to $167.21, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $163.22 to $163.54, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $163.55 to $164.54, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $164.56 to $165.54, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were traded by the Funds in multiple transactions at prices ranging from $165.59 to $166.58, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the Staff, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. Felix J. Baker is a director of Seattle Genetics, Inc. (the "Issuer"). By virtue of his 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 2020-05-08 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 2020-05-08 By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2020-05-08 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/ 2020-05-08 /s/ Felix J. Baker 2020-05-08 /s/ Julian C. Baker 2020-05-08