X0306 4 2016-09-06 0 0001060736 SEATTLE GENETICS INC /WA SGEN 0001087940 BAKER FELIX 667 MADISON AVENUE, 21ST FLOOR NEW YORK NY 10065 1 0 1 0 0001087939 BAKER JULIAN 667 MADISON AVENUE, 21ST FLOOR NEW YORK NY 10065 1 0 1 0 0001580575 Baker Bros. Advisors (GP) LLC 667 MADISION AVENUE, 21ST FLOOR NEW YORK NY New York 1 0 1 0 0001263508 BAKER BROS. ADVISORS LP 667 MADISON AVENUE, 21ST FLOOR NEW YORK NY 10065 1 0 1 0 0001551139 667, L.P. 667 MADISION AVENUE, 21ST FLOOR NEW YORK NY 10065 1 0 1 0 0001363364 Baker Brothers Life Sciences LP 667 MADISION AVENUE, 21ST FLOOR NEW YORK NY 10065 1 0 1 0 Common Stock 107511 D Common Stock 107504 D Common Stock 2016-09-06 4 P 0 9074 45.8037 A 4509054 I See footnote Common Stock 2016-09-06 4 P 0 2735 44.9819 A 4511789 I See footnote Common Stock 2016-09-06 4 P 0 8360 46.1022 A 4520149 I See footnote Common Stock 2016-09-06 4 P 0 35263 45.3863 A 4555412 I See footnote Common Stock 2016-09-06 4 P 0 3600 45.1026 A 4559012 I See footnote Common Stock 2016-09-06 4 P 0 84331 46.1709 A 4643343 I See Footnote Common Stock 2016-09-07 4 P 0 667 48.2853 A 4644010 I See Footnote Common Stock 2016-09-07 4 P 0 5930 48.2853 A 38793017 I See Footnote Common Stock 2016-09-07 4 P 0 967 48.4368 A 4644977 I See Footnote Common Stock 2016-09-07 4 P 0 8598 48.4368 A 38801615 I See Footnote Common Stock 2016-09-07 4 P 0 1314 48.1594 A 4646291 I See Footnote Common Stock 2016-09-07 4 P 0 11681 48.1594 A 38813296 I See Footnote Common Stock 2016-09-07 4 P 0 62 47.2697 A 4646353 I See Footnote Common Stock 2016-09-07 4 P 0 548 47.2697 A 38813844 I See Footnote Common Stock 2016-09-07 4 P 0 1457 48.9534 A 4647810 I See Footnote Common Stock 2016-09-07 4 P 0 12955 48.9534 A 38826799 I See Footnote Common Stock 2016-09-07 4 P 0 1556 48.6100 A 4649366 I See Footnote Common Stock 2016-09-07 4 P 0 13825 48.6100 A 38840624 I See Footnote Common Stock 2016-09-08 4 P 0 106 49.1810 A 4649472 I See Footnote Common Stock 2016-09-08 4 P 0 944 49.1810 A 38841568 I See Footnote Common Stock 2016-09-08 4 P 0 628 49.4589 A 4650100 I See Footnote Common Stock 2016-09-08 4 P 0 5581 49.4589 A 38847149 I See Footnote Common Stock 2016-09-08 4 P 0 11397 50.0487 A 4661497 I See Footnote Common Stock 2016-09-08 4 P 0 101290 50.0487 A 38948439 I See Footnote Common Stock 2016-09-08 4 P 0 5405 50.1047 A 4666902 I See Footnote Common Stock 2016-09-08 4 P 0 48036 50.1047 A 38996475 I See Footnote Common Stock 2016-09-08 4 P 0 3813 50.4778 A 4670715 I See Footnote Common Stock 2016-09-08 4 P 0 33893 50.4778 A 39030368 I See Footnote Reflects shares of common stock of Seattle Genetics, Inc. (the "Issuer") held directly by Felix J. Baker. Reflects shares of common stock of the Issuer held directly by Julian C. Baker. The price reported in Column 4 is a weighted average price. These shares were purchased by 667, L.P. ("667") in multiple transactions at prices ranging from $45.40 to $46.00, 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, 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 transactions reported herein and as a result of their ownership interest in Baker Biotech Capital (GP), LLC, Felix J. Baker and Julian C. Baker each may be deemed to have an indirect pecuniary interest in the Issuer's shares of 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 Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667. The price reported in Column 4 is a weighted average price. These shares were purchased by 667 in multiple transactions at prices ranging from $44.83 to $45.00, 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, 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 purchased by 667 in multiple transactions at prices ranging from $46.02 to $46.15, 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, 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 purchased by 667 in multiple transactions at prices ranging from $45.18 to $46.15, 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, 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 purchased by 667 in multiple transactions at prices ranging from $45.00 to $45.15, 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, 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 purchased by 667 in multiple transactions at prices ranging from $46.00 to $46.25, 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, 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 purchased by 667 and Baker Brothers Life Sciences, L.P. ("Life Sciences") in multiple transactions at prices ranging from $48.21 to $48.35, 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, 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 transactions reported herein and as a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in the Issuer's shares of 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 Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences The price reported in Column 4 is a weighted average price. These shares were purchased by 667 and Life Sciences in multiple transactions at prices ranging from $48.36 to $49.10, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $47.57 to $48.45, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $47.25 to $47.27, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $48.83 to $49.20, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $48.30 to $49.00, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $49.18 to $49.19, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $49.37 to $49.50, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $49.51 to $50.29, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $49.53 to $50.25, 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, 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 purchased by 667 and Life Sciences in multiple transactions at prices ranging from $50.46 to $50.50, 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, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote. Includes beneficial ownership of 14,400 previously issued restricted stock units payable solely in common shares 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 fund may be deemed to own a portion and 30,000 shares received previously from exercise of 30,000 stock options of the Issuer that were issued to Felix J. Baker in his capacity as a director of the Issuer, of which the fund may be deemed to own a portion. Baker Bros. Advisors LP (the "Adviser") serves as the Investment Adviser to Life Sciences and 667 (collectively 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 principals 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. 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. /s/ Felix J. Baker 2016-09-08 /s/ Julian C. Baker 2016-09-08 By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2016-09-08 By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 2016-09-08 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 2016-09-08 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 /s/ Scott L. Lessing 2016-09-08