NOTICE OF PENDENCY OF CLASS ACTION: Please be advised that your rights may be affected by the above-captioned securities class action (the “Action”) 1 pending in the United States District Court for the Southern District of New York (the “Court”), if, during the period between December 21, 2020, and August 17, 2021, inclusive (“Settlement Class Period”), you purchased or otherwise acquired Sesen Bio, Inc. (“Sesen Bio” or the “Company”) common stock (“Sesen Bio Common Stock”), and/or Sesen Bio call options (“Sesen Bio Call Options”), and/or wrote Sesen Bio put options (“Sesen Bio Put Options”), and were damaged thereby. 2

NOTICE OF SETTLEMENT: Please also be advised that the Court-appointed Lead Plaintiffs, Ryan Bibb, Rodney Samaan, Lionel Dreshaj, and Benjamin Dreshaj (collectively, “Lead Plaintiffs”), on behalfofthemselves and the Settlement Class (as defined in ,r 22 below), have reached a proposed settlement of the Action for $21,000,000 in cash that, if approved, will resolve all claims in the Action (the “Settlement”).