Welcome to our dedicated page for Mersana Therapeutics SEC filings (Ticker: MRSN), a comprehensive resource for investors and traders seeking official regulatory documents including 10-K annual reports, 10-Q quarterly earnings, 8-K material events, and insider trading forms.
Mersana Therapeutics filings document the regulatory record of a clinical-stage ADC developer and the corporate-status disclosures for its common stock. The company’s 8-K filings cover operating and financial results, clinical and regulatory updates, material agreements, shareholder voting matters, governance items, Nasdaq listing matters, and capital-structure actions such as amendments affecting common-stock rights.
Later filings include Form 25 removal of the common stock from Nasdaq listing and Form 15 certification to terminate or suspend Exchange Act reporting obligations. Those records document the company’s transition from an exchange-listed reporting company, including the registered security class and remaining holder information.
Day One Biopharmaceuticals plans a tender offer for all outstanding shares of Mersana Therapeutics via Emerald Merger Sub, its wholly owned subsidiary, as outlined in a Schedule TO-C. The communication relates solely to preliminary communications made before the commencement of the tender offer and is pursuant to an Agreement and Plan of Merger dated November 12, 2025.
The offer has not yet commenced. Upon commencement, Day One and the Purchaser will file a Schedule TO with an Offer to Purchase and Letter of Transmittal, and Mersana will file a Schedule 14D-9. The filing highlights forward-looking risks, including satisfaction of closing conditions, sufficient tenders, required regulatory approvals, potential competing offers, integration challenges, and the possibility that contingent value right milestones may not be achieved.
Day One Biopharmaceuticals agreed to acquire Mersana Therapeutics via a tender offer at $25.00 per share in cash plus one non‑tradable CVR per share with potential cash milestones of up to $30.25, for total consideration of up to $55.25 per share. The offer will remain open for 20 business days and will be followed by a Section 251(h) merger after successful completion.
Closing is expected by the end of January 2026, subject to customary conditions, including HSR clearance and a minimum tender of more than 50% of outstanding shares. There is no financing condition. Support agreements from specified holders covering approximately 8.5% of shares were executed. If certain termination events occur, Mersana would pay a $5.6 million termination fee. CVRs are contractual rights only and not equity, voting, or dividend-bearing.
Mersana Therapeutics entered a definitive agreement to be acquired by Day One Biopharmaceuticals via a tender offer. Holders of Mersana common stock will be offered $25.00 in cash per share, plus one CVR per share that may pay up to an additional $30.25 per share upon achieving specified milestones. The offer will remain open for 20 business days, subject to extension.
Completion requires that more than 50% of outstanding shares (by one share) are tendered (the Minimum Condition), HSR clearance, accuracy of representations and compliance with covenants; there is no financing condition. After the offer, a short-form merger under DGCL 251(h) would close, with all remaining shares converted into the same consideration. Closing is expected by the end of January 2026, subject to conditions. A termination fee of $5.6 million may be payable in specified circumstances. Support agreements cover approximately 8.5% of shares as of November 10, 2025. CVRs are non-transferable (with limited exceptions) and carry no voting or dividend rights.
Mersana Therapeutics (MRSN) insider activity: The SVP, Chief Development Officer reported RSU vesting of 250 shares of common stock on October 25, 2025, and an automatic sell-to-cover of 77 shares at $9.90 on October 27, 2025 under a Rule 10b5-1 trading plan adopted on May 10, 2023. Following these transactions, direct beneficial ownership is 2,922 shares.
The amounts reflect the one-for-twenty-five reverse stock split effected on July 25, 2025. Each RSU represented one common share, and the RSUs were fully vested as of October 25, 2025.
Mersana Therapeutics, Inc. reported that Nasdaq has notified the company it is not in compliance with Nasdaq Listing Rule 5450(b)(2)(A), which requires a minimum Market Value of Listed Securities of $50.0 million. This is a deficiency notice only and does not immediately affect the listing of Mersana’s common stock, which continues to trade on the Nasdaq Global Select Market under the symbol MRSN.
The company has 180 calendar days, until March 4, 2026, to regain compliance by having its market value close at or above $50.0 million for at least ten consecutive business days before that date. If Mersana does not regain compliance by the deadline, its securities would be subject to delisting, though it would have the right to appeal to a Nasdaq hearings panel. Mersana plans to monitor its market value and consider available options to address the issue, while noting there is no assurance it will regain or maintain compliance with Nasdaq rules.
Schonfeld Strategic Advisors LLC reported beneficial ownership of 5,673,852 shares of Mersana Therapeutics, Inc. (ticker MRSN), representing 4.55% of the company's common stock. The filing states Schonfeld has sole voting and sole dispositive power over all 5,673,852 shares and that these shares are held in accounts for clients, including separately managed accounts. The 4.55% figure is calculated using 124,631,339 shares outstanding as disclosed in Mersana's definitive proxy statement dated May 9, 2025. Schonfeld affirms the securities were acquired in the ordinary course of business and not to influence control of the issuer.
Mersana Therapeutics reported continued clinical progress on Emi-Le and XMT-2056 while facing clear financial strain. The company recorded a net loss of $24.3 million for the quarter and $48.4 million for the six months ended June 30, 2025, leaving an accumulated deficit of $944.0 million. Cash and cash equivalents declined to about $77.0 million at quarter end.
The report highlights encouraging interim Emi-Le activity, including a 31% confirmed ORR in B7-H4 high patients at intermediate doses and notable responses in adenoid cystic carcinoma and some TNBC and endometrial cohorts. The company also has meaningful collaboration balances, with deferred revenue around $98.6 million tied to GSK, Johnson & Johnson and Merck KGaA agreements. Management disclosed a strategic restructuring reducing headcount by ~55% and recorded $3.94 million of restructuring charges to focus resources on Emi-Le and select programs. The filing states there is substantial doubt about the company’s ability to continue as a going concern without additional financing.
Mersana Therapeutics announced a press release reporting business updates and financial results for the quarter ended June 30, 2025. The filing states the press release is furnished under Item 2.02 and that this furnished information, including Exhibit 99.1, is not to be deemed "filed" for purposes of Section 18 of the Exchange Act and is not incorporated by reference into other SEC filings except where specifically stated.
The Form 8-K lists Exhibit 99.1 (the press release) and Exhibit 104 (cover page interactive data) and is signed by the company’s Chief Financial Officer and Chief Operating Officer.
Mersana Therapeutics, Inc. (MRSN) has filed an 8-K disclosing that it will implement a 1-for-25 reverse stock split, effective 5:00 p.m. ET on 25 Jul 2025. Each block of 25 outstanding common shares will be reclassified into one share; fractional shares will be cashed out. The maneuver does not alter the company’s authorized share count or par value, but all equity incentive plan share pools and outstanding awards will be proportionally adjusted.
The reverse split is intended to restore compliance with Nasdaq’s $1.00 minimum bid price requirement, which the company previously flagged in its 2025 proxy. Post-split trading will commence on 28 Jul 2025 under the existing ticker “MRSN” with a new CUSIP of 59045L205.
No other material events, financial results or changes in fiscal year were reported. A copy of the Certificate of Amendment is attached as Exhibit 3.1.