Ownership Submission
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

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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(Print or Type Responses)
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 (Month/Day/Year)
04/30/2018
(Street)

NEW YORK, NY 10014
4. If Amendment, Date Original Filed(Month/Day/Year)
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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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               107,511 (1) D  
Common Stock               107,504 (2) D  
Common Stock 04/30/2018   P   154,218 A $ 50.9013 (11) 44,509,553 I See footnotes (6) (7) (12)
Common Stock 04/30/2018   P   248,121 A $ 51.0278 (13) 44,757,674 I See footnotes (6) (7) (12)
Common Stock 04/30/2018   P   52,700 A $ 51.0659 (14) 44,810,374 I See footnotes (6) (7) (12)
Common Stock 04/30/2018   P   168,097 A $ 51.2489 (15) 44,978,471 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   M   10,000 A $ 10.08 5,288,174 I See footnotes (3) (4) (6) (7) (8) (10)
Common Stock 05/01/2018   M   10,000 A $ 10.08 44,988,471 I See footnotes (4) (5) (6) (7) (8) (10)
Common Stock 05/01/2018   P   100,000 A $ 51.14 45,088,471 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   72,533 A $ 51.2552 (16) 45,161,004 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   22,700 A $ 51.2962 (17) 45,183,704 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   10,500 A $ 51.36 45,194,204 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   57,270 A $ 51.3656 (18) 45,251,474 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   37,963 A $ 52.0563 (19) 45,289,437 I See footnotes (6) (7) (12)
Common Stock 05/01/2018   P   5,951 A $ 52.3303 (20) 45,295,388 I See footnotes (6) (7) (12)
Common Stock 05/02/2018   P   2,000 A $ 51.875 45,297,388 I See footnotes (6) (7) (12)
Common Stock 05/02/2018   P   37,400 A $ 52.3268 (21) 45,334,788 I See footnotes (6) (7) (12)
Common Stock 05/02/2018   P   21,442 A $ 52.2608 (22) 45,356,230 I See footnotes (6) (7) (12)
Common Stock 05/02/2018   P   9,105 A $ 54.4193 (23) 45,365,335 I See footnotes (6) (7) (12)

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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 (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 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
(Month/Day/Year)
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 Options (right to buy) $ 10.08 04/30/2018   M     10,000 05/15/2009 05/16/2018 Common Stock 10,000 (9) 0 I See Footnotes (3) (10)
Non-Qualified Stock Options (right to buy) $ 10.08 04/30/2018   M     10,000 05/15/2009 05/16/2018 Common Stock 10,000 (9) 0 I See Footnotes (5) (10)

Reporting Owners

Reporting Owner Name / Address Relationships
 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   05/02/2018
**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   05/02/2018
**Signature of Reporting Person Date

 By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing   05/02/2018
**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/   05/02/2018
**Signature of Reporting Person Date

 /s/ Felix J. Baker   05/02/2018
**Signature of Reporting Person Date

 /s/ Julian C. Baker   05/02/2018
**Signature of Reporting Person Date

Explanation of Responses:

* 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).
(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 or principals of the Adviser to receive compensation for serving as a Director of the Issuer.
(4) 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).
(5) 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 (defined below) and the Adviser, does not permit full-time employees or principals of the Adviser to receive compensation for serving as a Director of the Issuer.
(6) Includes beneficial ownership of 18,100 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 50,000 shares, 40,000 of which were received previously, from exercise of 50,000 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.
(7) 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.
(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.
(11) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $50.71 to $51.00, 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 ("SEC"), upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(12) 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.
(13) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $50.91 to $51.40, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(14) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $50.67 to $51.47, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(15) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.01 to $52.00, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(16) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.07 to $51.46, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(17) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.10 to $51.72, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(18) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.27 to $51.46, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(19) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.54 to $52.50, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(20) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $52.00 to $52.50, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(21) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.91 to $52.88, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(22) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $51.88 to $52.76, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
(23) The price reported in Column 4 is a weighted average price. These shares were traded in multiple transactions at prices ranging from $54.40 to $54.42, inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the SEC, upon request, full information regarding the number of shares traded at each separate price within the range set forth in this footnote.
 
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.

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