Sec Form 4 Filing - BAKER BROS. ADVISORS LP @ Seagen Inc. - 2023-12-14

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 _____ 10% Owner _____ Officer (give title below) X __ Other (specify below) Former 10% Owner (Last) (First) (Middle) 860 WASHINGTON STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 12/14/2023 (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 12/14/2023 D( 1 ) 23,280 ( 1 ) D $ 229 ( 1 ) ( 2 ) 0 ( 3 ) D Common Stock 12/14/2023 D( 1 ) 23,277 ( 1 ) D $ 229 ( 1 ) ( 2 ) 0 ( 4 ) D Common Stock 12/14/2023 D( 1 ) 1,731,202 ( 1 ) D $ 229 ( 1 ) ( 2 ) ( 5 ) ( 6 ) 0 I See Footnotes ( 7 ) ( 8 ) ( 9 ) ( 10 ) ( 11 ) ( 12 ) Common Stock 12/14/2023 D( 1 ) 42,977,301 ( 1 ) D $ 229 ( 1 ) ( 2 ) ( 5 ) ( 6 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) ( 12 ) ( 13 )

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 Stock Options (right to buy) $ 34.25 12/14/2023 D( 1 ) 8,750 ( 14 ) 05/16/2024 Common Stock 8,750 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 39.94 12/14/2023 D( 1 ) 9,260 ( 14 ) 05/15/2025 Common Stock 9,260 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 38.82 12/14/2023 D( 1 ) 9,260 ( 14 ) 05/20/2026 Common Stock 9,260 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 66.6 12/14/2023 D( 1 ) 9,260 ( 14 ) 05/19/2027 Common Stock 9,260 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 56.77 12/14/2023 D( 1 ) 9,260 ( 14 ) 05/18/2028 Common Stock 9,260 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 64.38 12/14/2023 D( 1 ) 7,038 ( 14 ) 05/20/2029 Common Stock 7,038 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 160.33 12/14/2023 D( 1 ) 3,371 ( 14 ) 05/15/2030 Common Stock 3,371 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 147.5 12/14/2023 D( 1 ) 3,462 ( 14 ) 05/14/2031 Common Stock 3,462 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 ) Stock Options (right to buy) $ 135.63 12/14/2023 D( 1 ) 3,676 ( 14 ) 05/13/2032 Common Stock 3,676 ( 14 ) 0 I See Footnotes ( 8 ) ( 9 ) ( 10 ) ( 11 )

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 Former 10% Owner 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Former 10% Owner BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Former 10% Owner BAKER FELIX 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Former 10% Owner Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Former 10% Owner Baker Brothers Life Sciences LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Former 10% Owner Signatures By: Baker Bros. Advisors LP, Name: Scott L.Lessing, Title: President /s/ Scott L. Lessing 12/18/2023 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 12/18/2023 Signature of Reporting Person Date /s/ Julian C. Baker 12/18/2023 Signature of Reporting Person Date /s/ Felix J. Baker 12/18/2023 Signature of Reporting Person Date By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 12/18/2023 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/ 12/18/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Reflects the disposition of shares of common stock ("Common Stock"), of Seagen Inc. (the "Issuer"), or of options to purchase Common Stock ("Stock Options"), as applicable, in connection with the consummation of the transactions contemplated by the Agreement and Plan of Merger, dated as of March 12, 2023 (the "Merger Agreement"), by and among the Issuer, Pfizer Inc. ("Parent") and Aris Merger Sub, Inc. ("Merger Sub"), a wholly owned subsidiary of Parent, pursuant to which, at the effective time of the Merger on December 14, 2023 (the "Effective Time"), Merger Sub merged with and into the Issuer, with the Issuer surviving as a subsidiary of Parent (the "Merger"). ( 2 )Pursuant to the Merger Agreement, at the Effective Time, each issued and outstanding share of Common Stock (other than certain excluded shares described in the Merger Agreement) was converted into the right to receive cash in an amount equal to $229.00 per share of Common Stock (the "Merger Consideration"). ( 3 )Reflects shares of Common Stock held directly by Felix J. Baker. ( 4 )Reflects shares of Common Stock held directly by Julian C. Baker. ( 5 )Pursuant to the Merger Agreement, at the Effective Time, 29,003 vested restricted stock units (each, an "RSU"), held by Felix J. Baker were converted into the right to receive an amount in cash equal to the product of (i) the Merger Consideration, multiplied by (ii) the number of shares of Common Stock then subject to such RSU, net of applicable taxes and without interest. ( 6 )Pursuant to the Merger Agreement, at the Effective Time, each of the 2,044 RSUs granted to Felix J. Baker on May 31, 2023 that were unvested as of immediately prior to the Effective Time (each, a "Post-Signing Company RSU") were converted into the right to receive a Parent cash-based award subject to service-based vesting requirements with respect to an amount in cash equal to the product of (i) the Merger Consideration, multiplied by (ii) the number of shares of Common Stock then subject to such Post-Signing Company RSU. ( 7 )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 have been deemed to have had an indirect pecuniary interest in Common Stock 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. ( 8 )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 ofthe Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held by the Funds. ( 9 )Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities that were held directly by the Funds exceptto 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, theAdviser GP or the Adviser was a beneficial owner of such securities for purposes of Section 16 or any other purpose. ( 10 )Pursuant to agreements between Felix J. Baker and the Adviser, the Adviser had voting and dispositive power over Stock Options, RSUs and any Common Stock received as a result of the exercise of Stock Options or vesting of RSUs. ( 11 )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 feesand the Funds are entitled to an indirect proportionate pecuniary interest in such securities. The Funds each owned an indirect proportionatepecuniary 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 have been deemed to have had an indirect pecuniary interest in the shares of Common Stock issued inlieu of director retainer fees, Stock Options, Common Stock issued upon exercise of Stock Options, RSUs and Common Stock rece ived upon vesting of RSUs (ie. no direct pecuniary interest). ( 12 )Includes beneficial ownership of 31,047 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 121,250 previously issued shares of Common Stock from exercise of 121,250 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. ( 13 )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 have been deemed to have had an indirect pecuniary interest in Common Stock 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. ( 14 )Pursuant to the Merger Agreement, each outstanding Stock Option, whether or not then vested, was cancelled in exchange for the right to receive an amount in cash equal to the product of (i) the excess, if any, of the Merger Consideration over the per-share exercise price of such option, multiplied by (ii) the number of shares of Common Stock then subject to such Stock Option.

Remarks: Felix J. Baker was 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 were deemed directors by deputization of the Issuer.

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