Statement of Changes in Beneficial Ownership (4)

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 OF SECURITIES	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response... 0.5
	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person ^* BAKER BROS. ADVISORS LP	2. Issuer Name and Ticker or Trading Symbol SEATTLE GENETICS INC /WA [ 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/YYYY) 4/29/2019
(Street) NEW YORK, NY 10014 (City) (State) (Zip)	4. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	3. Trans. 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)
1.Title of Security (Instr. 3)	2. Trans. Date	2A. Deemed Execution Date, if any	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Stock								107511 ⁽¹⁾	D
Common Stock								107504 ⁽²⁾	D
Common Stock	4/29/2019		M		10000	A	$8.38	5301874	I	See footnotes ⁽³⁾ ⁽⁴⁾ ⁽⁵⁾ ⁽⁷⁾ ⁽⁸⁾ ⁽¹⁰⁾
Common Stock	4/29/2019		M		10000	A	$8.38	45839686	I	See footnotes ⁽⁴⁾ ⁽⁵⁾ ⁽⁶⁾ ⁽⁷⁾ ⁽⁸⁾ ⁽¹⁰⁾

*Table II - Derivative Securities Beneficially Owned ( e.g.* , puts, calls, warrants, options, convertible securities)**
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	4. Trans. 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		7. Title and Amount of Securities Underlying Derivative Security (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)
1. Title of Derivate Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Trans. Date	3A. Deemed Execution Date, if any	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)			11. Nature of Indirect Beneficial Ownership (Instr. 4)
Non-Qualified Stock Options (right to buy)	$8.38	4/29/2019		M			10000	5/14/2010	5/15/2019	Common Stock	10000	⁽⁹⁾	0	I	See Footnotes ⁽³⁾ ⁽¹⁰⁾
Non-Qualified Stock Options (right to buy)	$8.38	4/29/2019		M			10000	5/14/2010	5/15/2019	Common Stock	10000	⁽⁹⁾	0	I	See Footnotes ⁽⁶⁾ ⁽¹⁰⁾

Explanation of Responses:
(1)	Reflects shares of common stock of Seattle Genetics, Inc. (the "Issuer") held directly by Felix J. Baker.
(2)	Reflects shares of common stock of the Issuer held directly by Julian C. Baker.
(3)	As a result of their ownership interest in Baker Biotech Capital (GP), LLC, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in 10,000 shares of Common Stock of the Issuer received upon the exercise of stock options of the Issuer held by 667, L.P. ("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 policy of the Funds (defined below) and Baker Bros. Advisors LP (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)	The Adviser serves as the Investment Adviser to Baker Brothers Life Sciences, L.P. 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 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.
(5)	The shares of common stock were received upon exercise of 10,000 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 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 shares of common stock received upon exercise of such stock options. Each of the Funds owns an indirect proportionate pecuniary interest in the shares of common stock received upon exercise of the stock options issued in connection with Felix J. Baker's service on the Board less the exercise cost of those options. Solely as a result of their ownership interest in the general partners of the general partners of the Funds, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in the shares issued upon exercise of the stock options (i.e. no direct pecuniary interest).
(6)	As a result of their ownership interest in Baker Brothers Life Sciences Capital (GP), LLC, Felix J. Baker and Julian C. Baker may be deemed to have an indirect pecuniary interest in 10,000 shares of Common Stock of the Issuer received upon the exercise of stock options of the Issuer held by Baker Brothers Life Sciences, L.P. ("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 policy of the Funds and the Adviser, does not permit full-time employees of the Adviser or principals of the Adviser GP to receive compensation for serving as a Director of the Issuer.
(7)	Includes beneficial ownership of 21,800 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 Funds may be deemed to own a portion and 60,000 shares, 50,000 of which were received previously, from exercise of 60,000 stock options of the Issuer that were issued to Felix J. Baker in his capacity as a director of the Issuer, of which the Funds may be deemed to own a portion.
(8)	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.
(9)	These non-qualified stock options are not priced.
(10)	The disclosure of the exercise of directors options for shares of common stock reported on this form is a single exercise of 10,000 shares. The 10,000 shares are reported for each of the Funds as each has an indirect pecuniary interest.

Remarks:
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.

Reporting Owners
Reporting Owner Name / Address	Relationships
Reporting Owner Name / Address	Director	10% Owner	Officer	Other
BAKER BROS. ADVISORS LP 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY 10014	X	X
667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY 10014	X	X
Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY 10014	X	X
Baker Brothers Life Sciences LP 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY 10014	X	X
BAKER FELIX 860 WASHINGTON STREET 3RD FLOOR NEW YORK, NY 10014	X	X
BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY 10014	X	X

Signatures
By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing		5/1/2019
^** 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		5/1/2019
^** Signature of Reporting Person		Date
By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing		5/1/2019
^** 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/		5/1/2019
^** Signature of Reporting Person		Date
/s/ Felix J. Baker		5/1/2019
^** Signature of Reporting Person		Date
/s/ Julian C. Baker		5/1/2019
^** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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