Seattle Genetics Inc (SGEN): Baker Bros. Advisors Raises Stake

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Page 16 of 16 – SEC Filing

SIGNATURE

After reasonable inquiry and to the best of
my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

September 15, 2016

BAKER BROS. ADVISORS LP
By:  Baker Bros. Advisors (GP) LLC,
its general partner
By: /s/ Scott L. Lessing
Name: Scott L. Lessing
Title:   President
BAKER BROS. ADVISORS (GP) LLC
By: /s/ Scott L. Lessing
Name: Scott L. Lessing
Title:   President
    /s/ Julian C. Baker
      Julian C. Baker
    /s/ Felix J. Baker
      Felix J. Baker
FBB2, LLC
By: /s/ Julian C. Baker
Name: Julian C. Baker
Title:   Manager
FBB3 LLC
By: /s/ Julian C. Baker
Name: Julian C. Baker
Title:   Manager
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