SELLING STOCKHOLDERS
The selling stockholders named in this prospectus may offer and sell up to 47,366,002 shares of our common stock. Other than disclosed herein, the foregoing
shares represent all shares of common stock reported to us as held by the selling stockholders as of December 15, 2020.
On September 10, 2015,
in connection with a follow-on public offering of our common stock, we entered into a Registration Rights Agreement with the selling stockholders, pursuant to which we agreed that, if the selling stockholders
demand that we register their shares of our common stock for resale under the Securities Act, we would be obligated to effect such registration. Our registration obligations under this Registration Rights Agreement cover all shares of our common
stock now held or later acquired by the selling stockholders, will continue in effect for up to 10 years from the date of the Registration Rights Agreement, and include our obligation to facilitate certain underwritten public offerings of our common
stock by the selling stockholders in the future. We have agreed to bear all expenses incurred by us in effecting any registration pursuant to the Registration Rights Agreement as well as the legal expenses of the selling stockholders of up to
$50,000 per underwritten public offering effected pursuant to the Registration Rights Agreement. Additional information with respect to the Registration Rights Agreement is contained in our current report on Form
8-K filed with the SEC on September 11, 2015. On July 26, 2018, pursuant to the Registration Rights Agreement, we previously registered for resale, from time to time, up to 50,977,960 shares of our
common stock held by the selling stockholders. The resale of these shares was covered by a prior prospectus and related prospectus supplement dated July 26, 2018, or together, the prior prospectus. The common stock covered by the prior
prospectus will no longer be offered and sold under the prior prospectus, but will instead be offered and sold under this prospectus.
Felix J. Baker, a
director of Seagen, is a principal of the sole general partner of Baker Bros. Advisors LP, or BBA, which may be deemed to have the power to vote or direct the vote of and the power to dispose or direct the disposition of the shares of common stock
registered for resale pursuant to this prospectus and thus may be deemed the beneficial owner of such shares of common stock. Entities affiliated with Felix J. Baker and BBA, or the Baker Entities, purchased an aggregate of 3,846,153 of the shares
of common stock offered in the follow-on public offering we completed in February 2018 at the public offering price of $52.00 per share, for an aggregate purchase price of approximately $200 million. The
shares purchased in these follow-on public offerings are included in the shares of common stock offered by this prospectus.
In November 2019, we entered into a license agreement with BeiGene, Ltd., or BeiGene, for the advancement of a preclinical product candidate for treating
cancer. Felix J. Baker and the Baker Entities owned 13.0% of BeiGene as of December 4, 2020, according to the Schedule 13-D/A filed by the Baker Entities on December 4, 2020. In addition, two
representatives of the Baker Entities serve on BeiGenes board of directors. Seagen received an upfront payment of $20 million and is eligible to receive progress-dependent milestones for total potential upfront and milestone payments of
up to $160 million, as well as royalties for potential sales of the product candidate.
Except for beneficial ownership of our securities, the
Registration Rights Agreement, Felix J. Bakers position on our Board of Directors, the participation by entities affiliated with Felix J. Baker and BBA in our 2018 public offering and the license agreement with BeiGene, the selling
stockholders have not had any material relationship with us or our affiliates within the past three years.
The table below, including the footnotes,
lists the selling stockholders and other information regarding the beneficial ownership of the shares of common stock held by the selling stockholders based on information provided to us by the selling stockholders. Generally, a person
beneficially owns shares of our common stock if the person has or shares with others the right to vote those shares or to dispose of them, or if the person has the right to acquire voting or disposition rights within 60 days. The
percentages of shares owned prior to and after the offering are based on 180,895,399 shares of our common stock outstanding as of December 24, 2020, which includes the outstanding shares of common stock offered by this prospectus and other
shares reported to us as
9.