On November 14, 2025 Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on the development of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, reported a business update and announced financial results for the third quarter ended September 30, 2025.

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Acquisition by Day One Biopharmaceuticals, Inc.

Yesterday, Mersana announced that it has entered into a definitive merger agreement with Day One Biopharmaceutics, Inc. (Day One), pursuant to which Day One would acquire Mersana, through a tender offer followed by a second step merger, for upfront consideration of $25.00 per share in cash plus up to an aggregate of $30.25 per share in cash potentially payable under contingent value rights (CVRs) triggered upon the achievement of certain clinical development, regulatory and commercial milestones related to Emi-Le, the company’s B7-H4-directed Dolasynthen ADC, and upon the achievement of a certain milestone pursuant to an existing Mersana collaboration to be issued in the proposed acquisition, representing a total equity value of approximately $129 million at closing and representing a total deal value of up to approximately $285 million. Closing of the transaction is subject to the satisfaction of customary closing conditions, including that a majority of Mersana’s shares of common stock are validly tendered in the tender offer and not validly withdrawn and the receipt of certain U.S. regulatory approvals, and is expected to occur by the end of January 2026.

Emiltatug Ledadotin (Emi-Le; XMT-1660)
In the ongoing Phase 1 clinical trial of Emi-Le, Mersana continues to follow patients in its two dose expansion cohorts in patients with triple-negative breast cancer, or TNBC, who have received one to four prior treatment lines in the locally advanced or metastatic setting, including at least one prior topoisomerase-1 inhibitor ADC.

Mersana is also evaluating Emi-Le in patients with adenoid cystic carcinoma type 1 (ACC-1), a population with very high unmet need, in the backfill cohorts of the dose escalation portion of the ongoing Phase 1 clinical trial. In June 2025, at ASCO (Free ASCO Whitepaper), Mersana presented interim clinical data from nine evaluable patients with ACC-1. As of October 1, 2025, Mersana has enrolled a substantially greater number of ACC-1 patients in these backfill cohorts than was presented at ASCO (Free ASCO Whitepaper). The data from ACC-1 patients enrolled in this trial continues to mature as Mersana enrolls additional patients and patients remain on treatment for longer periods. Mersana has continued to be encouraged by the responses of the patients in these backfill cohorts.

Emi-Le continues to be generally well-tolerated, and its observed safety profile remains consistent with previously disclosed data.

XMT-2056
Mersana’s Phase 1 clinical trial of XMT-2056, the company’s lead Immunosynthen ADC candidate targeting a novel HER2 epitope, is ongoing. In the third quarter of 2025, Mersana achieved and received a $15 million development milestone under its agreement with GSK plc (GSK), which has an exclusive global license option to co-develop and commercialize XMT-2056.

Collaborations
Mersana continues to support its collaborations with both Janssen Biotech, Inc. (Johnson & Johnson, Dolasynthen research collaboration) and Merck KGaA, Darmstadt, Germany (Immunosynthen research collaboration).

In the third quarter of 2025, Johnson & Johnson received clearance from the U.S. Food and Drug Administration (FDA) of an investigational new drug application for a Dolasynthen ADC developed under Mersana’s 2022 collaboration and license agreement with Johnson & Johnson. An $8.0 million development milestone is associated with the further progress of this first-in-human clinical trial pursuant to the agreement with Johnson & Johnson.

Third Quarter 2025 Financial Results and Recent Updates

Net cash used in operating activities for the third quarter of 2025 was $3.2 million, which reflects the impact of the $15 million GSK development milestone payment received.
Cash and cash equivalents as of September 30, 2025 were $56.4 million. The company continues to expect that its capital resources will be sufficient to support its current operating plan commitments into mid-2026.
Collaboration revenue for the third quarter of 2025 was $11.0 million, compared to $12.6 million for the same period in 2024. The year-over-year change was primarily related to decreased revenue recognized under the company’s collaboration and license agreements with Johnson & Johnson and Merck KGaA, Darmstadt, Germany, partially offset by increased revenue recognized under its agreement with GSK.
Research and development (R&D) expense for the third quarter of 2025 was $12.2 million, compared to $14.8 million for the same period in 2024. Included in the third quarter of 2025 R&D expense was $0.5 million in non-cash stock-based compensation expense. The year-over-year change in R&D expense was primarily related to lower headcount and related employee compensation costs, partially offset by an increase in costs related to Emi-Le and XMT-2056 clinical development activities.
General and administrative (G&A) expense for the third quarter of 2025 was $6.3 million, compared to $9.9 million during the same period in 2024. Included in the third quarter of 2025 G&A expense was $0.6 million in non-cash stock-based compensation expenses. The year-over-year change in G&A expense was primarily related to lower headcount and related employee compensation costs and a reduction in consulting and professional services fees.
Net loss for the third quarter of 2025 was $7.5 million, or $1.51 per share, compared to a net loss of $11.5 million, or $2.34 per share, for the same period in 2024.
Conference Call
Mersana’s previously scheduled conference call to discuss business updates and its financial results for the third quarter of 2025 has been cancelled.

(Press release, Mersana Therapeutics, NOV 14, 2025, View Source [SID1234659975])