BAKER BROS. ADVISORS LP - 14 Dec 2023 Form 4 Insider Report for Seagen Inc.

Footnote F1

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").

Footnote F2

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").

Footnote F3

Reflects shares of Common Stock held directly by Felix J. Baker.

Footnote F4

Reflects shares of Common Stock held directly by Julian C. Baker.

Footnote F5

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.

Footnote F6

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.

Footnote F7

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.

Footnote F8

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.

Footnote F9

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 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 was a beneficial owner of such securities for purposes of Section 16 or any other purpose.

Footnote F10

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.

Footnote F11

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 such securities. The Funds each owned 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 have been deemed to have had 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).

Footnote F12

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.

Footnote F13

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.

Footnote F14

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.