Failure to Satisfy Listing Rule (Form 8-K)

Item 3.01 Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing.

On September 5, 2025, Mersana Therapeutics, Inc. (the "Company") received written notice (the "Notice") from the Listing Qualifications Department of The Nasdaq Stock Market LLC ("Nasdaq") notifying the Company that the Company is not in compliance with Nasdaq Listing Rule 5450(b)(2)(A) (the "MVLS Rule"), which requires the Company to maintain a minimum Market Value of Listed Securities ("MVLS") of $50.0 million. The Notice is only a notification of deficiency, not of imminent delisting, and has no current effect on the listing of the Company's common stock, which continues to trade on The Nasdaq Global Select Market under the symbol "MRSN."

In accordance with the MVLS Rule, the Company has a period of 180 calendar days, or until March 4, 2026 (the "Compliance Date"), to regain compliance with the MVLS Rule. To regain compliance, the Company's MVLS must close at $50.0 million or more for a minimum of ten consecutive business days prior to the Compliance Date. In the event the Company does not regain compliance with the MVLS Rule prior to the Compliance Date, Nasdaq will notify the Company that its securities are subject to delisting. At that time, the Company will have the opportunity to appeal the delisting determination to a Nasdaq hearings panel. The Company intends to monitor its MVLS and consider its available options to regain compliance with the MVLS Rule. However, there can be no assurance that the Company will be able to regain compliance with the MVLS Rule or maintain compliance with other Nasdaq listing rules.