Sec Form 4 Filing - BAKER BROS. ADVISORS LP @ Seagen Inc. - 2023-05-01

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person BAKER BROS. ADVISORS LP 2. Issuer Name and Ticker or Trading Symbol Seagen Inc. [ SGEN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 860 WASHINGTON STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 05/01/2023 (Street) NEW YORK, NY10014 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/01/2023 M 8,750 A $ 36.7 4,097,515 I See footnotes ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) Common Stock 05/01/2023 M 8,750 A $ 36.7 42,975,257 I See footnotes ( 1 ) ( 2 ) ( 3 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Common Stock 05/01/2023 J 2,368,357 D $ 0 1,729,158 I See footnotes ( 2 ) ( 3 ) ( 4 ) ( 6 ) ( 7 ) ( 8 ) ( 10 ) Common Stock 05/01/2023 J 209,175 A $ 0 232,455 ( 11 ) D Common Stock 05/01/2023 J 209,175 A $ 0 232,452 ( 12 ) D Common Stock 05/02/2023 G 209,175 D $ 0 23,280 ( 13 ) D Common Stock 05/02/2023 G 209,175 D $ 0 23,277 ( 14 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Non-Qualified Stock Option (right to buy) $ 36.7 05/01/2023 M 8,750 05/16/2014 05/16/2023 Common Stock 8,750 $ 0 0 I See footnotes ( 1 ) ( 2 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) Non-Qualified Stock Option (right to buy) $ 36.7 05/01/2023 M 8,750 05/16/2014 05/16/2023 Common Stock 8,750 $ 0 0 I See footnotes ( 1 ) ( 2 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAKER BROS. ADVISORS LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X Baker Brothers Life Sciences LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X BAKER FELIX 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X X Signatures By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 05/03/2023 Signature of Reporting Person Date 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/ 05/03/2023 Signature of Reporting Person Date 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 05/03/2023 Signature of Reporting Person Date Julian C. Baker 05/03/2023 Signature of Reporting Person Date Felix J. Baker 05/03/2023 Signature of Reporting Person Date By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 05/03/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Common Stock ("Common Stock") of Seagen Inc. (the "Issuer") acquired upon exercise of 8,750 non-qualified stock options exercisable into Common Stock on a 1-for-1 basis ("Stock Options") that were issued to Felix J. Baker in his capacity as a director of the Issuer. Felix J. Baker, pursuant to the policies of Baker Bros. Advisors LP (the "Adviser"), does not have any right to the pecuniary interest in the Stock Options issued for his service on the board of directors of the Issuer (the "Board") or the Common Stock acquired upon exercise of such Stock Options. Each of 667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds") owns an indirect proportionate pecuniary interest in the Common Stock acquired upon exercise of the Stock Options issued in connection with Felix J. Baker's service on the Board less the exercise cost of those Stock Options. ( 2 )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, restricted stock units (each an "RSU") payable solely in Common Stock and Common Stock received upon vesting of RSUs (i.e. no direct pecuniary interest). ( 3 )Includes beneficial ownership of 29,003 previously issued RSUs payable solely in Common Stock issued to Felix Baker in his capacity as a director of the Issuerpursuant 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 fromexercise 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. ( 4 )After giving effect to the transactions 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. ( 5 )The disclosure of the exercise of Stock Options for Common Stock reported on this form is a single exercise of 8,750 Stock Options. The exercise of 8,750 StockOptions is reported for each of the Funds as each has an indirect pecuniary interest in such securities. ( 6 )The Adviser serves as the investment adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-basedmanagement 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 andauthority 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 alldiscretion and authority with respect to the investment and voting power of the securities held by the Funds. ( 7 )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. ( 8 )Pursuant to agreements between Felix J. Baker and the Adviser, the Adviser has voting and dispositive power over the Stock Options, RSUs and any Common Stock received as a result of the exercise of Stock Options or vesting of RSUs. ( 9 )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. ( 10 )Represents shares of Common Stock distributed by 667 as part of an in-kind pro rata distribution without consideration in accordance with pecuniary interest to Julian C. Baker, Felix J. Baker and other investors in 667. ( 11 )Common Stock held directly by Felix J. Baker, including 209,175 shares of Common Stock received from the in-kind pro rata distribution by 667 without consideration reported above. ( 12 )Common Stock held directly by Julian C. Baker, including 209,175 shares of Common Stock received from the in-kind pro rata distribution by 667 without considerationreported above. ( 13 )Reflects shares of Common Stock of the Issuer held directly by Felix J. Baker. ( 14 )Reflects Common Stock held directly by Julian C. Baker.

Remarks: Felix J. Baker is a director of Seagen 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 other than Felix J. Baker are deemed directors by deputization of the Issuer.

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