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Julian Baker and Felix Baker

Seattle Genetics Inc. (NASDAQ:SGEN) is the subject of a new 13D filing issued by Julian Baker and Felix Baker‘s Baker Bros. Advisors, by far the top shareholder of the stock in our database at the end of December. The filing reveals that the healthcare-focused fund has purchased just over 1.00 million shares of Seattle Genetics over the past few days and that its ownership is up to 39.81 million shares in total, 28.4% of the company’s stock. The filing and latest ownership information are embedded below.

You can access the original SEC filing by clicking here.

Ownership Summary Table

Name Sole Voting Power Shared Voting Power Sole Dispositive Power Shared Dispositive Power Aggregate Amount Owned Power Percent of Class
Baker Bros. Advisors 39,674,346 0 39,674,346 0 39,674,346 28.3%
Baker Bros. Advisors (GP) 39,674,346 0 39,674,346 0 39,674,346 28.3%
Julian C. Baker 39,812,771 0 39,812,771 0 39,812,771 28.4%
Felix J. Baker 39,812,778 0 39,812,778 0 39,812,778 28.4%
FBB 18,243 0 18,243 0 18,243  The percentage of ownership is less than 0.1%
FBB3 12,678 0 12,678 0 12,678  The percentage of ownership is less than 0.1%
Julian Baker And Felix Baker
Julian Baker And Felix Baker
Baker Bros. Advisors

Page 1 of 11 SEC Filing

Washington, D.C. 20549

Under the Securities Exchange Act of 1934

(Amendment No. 18)

Seattle Genetics, Inc.
(Name of Issuer)
Common Stock, par value $0.001 per share
(Title of Class of Securities)
(CUSIP Number)

Alexandra A. Toohey

Chief Financial Officer

Baker Bros. Advisors LP
667 Madison Avenue, 21st Floor
New York, NY 10065
(212) 339-5690

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)
February 22, 2016
(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed
a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because
of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box. ¨

Note: Schedules filed in paper format
shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom
copies are to be sent.

*The remainder of this cover page shall
be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for
any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder
of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of
1934 (the “Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other
provisions of the Act (however, see the Notes).

Page 1 of 11 Pages
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