Financial Data and Key Metrics - Collaboration revenue for Q4 2023 was $10.7 million, down from $14.7 million in Q4 2022, primarily due to the timing of research activities and the achievement of an early development milestone with Johnson & Johnson in Q4 2022 [10] - General and administrative expenses for Q4 2023 were $10.1 million, compared to $14.8 million in Q4 2022, with $1.9 million in non-cash stock-based compensation expenses included [11] - Research and development expenses for Q4 2023 were $21.5 million, down from $45.7 million in Q4 2022, driven by reduced manufacturing and clinical costs related to UpRi and XMT-2056, and lower employee compensation costs [99] - Net loss for Q4 2023 was $19.5 million, compared to a net loss of $44.9 million in Q4 2022 [100] - The company ended Q4 2023 with approximately $209 million in cash, cash equivalents, and marketable securities, with net cash used in operating activities at $32 million, down significantly from prior quarters due to restructuring and UpRi wind-down efforts [98] Business Line Data and Key Metrics - The company is advancing its Dolasynthen ADC platform, with XMT-1660 (B7-H4 targeting ADC) in Phase 1 trials, currently at a dose of 59 mg/m², the highest dose investigated clinically with Dolasynthen ADC [6][81] - XMT-2056, the lead Immunosynthen ADC targeting HER2, is in the process of restarting its Phase 1 trial after a clinical hold by the FDA in Q4 2023 [70] - The company has collaboration agreements with Johnson & Johnson, Merck KGaA, and GSK, focusing on maximizing the potential of its ADC platforms and product candidates [8] Market Data and Key Metrics - The company is targeting solid tumors, including triple-negative breast cancer, estrogen receptor-positive breast cancer, ovarian cancer, and endometrial cancer, with XMT-1660 [68] - For XMT-2056, the company plans to enroll patients with HER2-positive tumors, including breast, gastric, colorectal, and non-small cell lung cancer [70] Company Strategy and Industry Competition - The company aims to minimize dose-limiting platform toxicities, avoid resistance mechanisms, and extend ADC therapies beyond cytotoxics to include targeted innate immune responses [3][4] - The Dolasynthen platform is designed to avoid dose-limiting neutropenia and peripheral neuropathy associated with other ADC platforms, such as vcMMAE [57][66] - The company believes its Immunosynthen platform, which harnesses STING, could be the next significant frontier for ADCs, offering potential for combination therapies with other standard-of-care treatments [7][113] Management Commentary on Operating Environment and Future Outlook - The company is optimistic about its differentiated ADC platforms and upcoming data readouts, particularly for XMT-1660, and believes its cash runway will support operations into 2026 [97][72] - Management highlighted the urgent unmet need for new ADCs with alternative payloads, as resistance to TOPO1-ADC treatments is emerging in breast cancer patients [69] Other Important Information - The company will present clinical data for discontinued candidates UpRi and XMT-1592 at the European Society of Gynecological Oncology (ESGO) conference, with 31 patients in the XMT-1592 dataset [5][114] - The company is exploring alternative dosing schedules for XMT-1660, including Q3 and Q4 schedules, to optimize dosing [81] Q&A Session Summary Question: Decision-making process behind the second-gen NaPi2b program and lessons for B7-H4 program [15] - The decision to reprioritize XMT-1592 was driven by the lower prevalence of the NaPi2b biomarker in lung cancer compared to ovarian cancer, as well as cost considerations [79][16] - For B7-H4, the company has not observed pneumonitis, which was associated with NaPi2b, and is continuing to optimize dosing and enrollment [80][81] Question: Enrollment progress and dose optimization for B7-H4 study [15] - The company has escalated to a dose of 59 mg/m² for XMT-1660 and is continuing to enroll patients in backfill cohorts to optimize dosing [81] Question: Expectations for midyear 1660 update and takeaways from 1592 data [101] - The midyear update for XMT-1660 will include efficacy and safety data, with the company highlighting the absence of peripheral neuropathy, neutropenia, and ocular toxicity observed in XMT-1592 [13][14] Question: Cash runway and expense trajectory [54] - The company expects its cash runway to support operations into 2026, with reduced OpEx in Q4 2023 and the completion of UpRi wind-down efforts [34][72] Question: B7-H4 biomarker and potential biomarker data in midyear update [41] - The company is measuring B7-H4 at baseline but not preselecting patients based on it, and has not decided whether to share biomarker data in the midyear update [128] Question: Differentiation and positioning of XMT-1660 compared to peers [133] - The company believes its Dolasynthen platform offers advantages in terms of lower toxicity and potential for combination therapies, with a focus on triple-negative breast cancer and other solid tumors [123][135] Question: Restarting the XMT-2056 trial and GSK's involvement [111] - The company is in the process of restarting the XMT-2056 trial, with GSK engaged but not having exercised its option, leaving decision-making control with the company [86][109] Question: Duration of response and resistance mechanisms in breast cancer [30][52] - The company is cautious about interpreting duration of response in Phase 1 data but notes that patients who responded to UpRi had a duration of response over seven months [31][137] - The company is enrolling patients who have received prior TOPO ADCs to assess resistance mechanisms and the efficacy of XMT-1660 [60][52]

Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2023. OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-38129 Mersana Therapeutics, Inc. (Exact name of registrant as specified in its charter) Delaware 04-3562403 (State ...

Exhibit 99.1 Mersana Therapeutics Provides Business Update and Announces Fourth Quarter and Full Year 2023 Financial Results CAMBRIDGE, Mass., February 28, 2024 – Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, today provided a business update and reported financial results for the fourth quarter and full year ended December 31, 2023 ...

Mersana Therapeutics, Inc. (NASDAQ:MRSN) Q3 2023 Earnings Conference Call November 7, 2023 8:00 AM ET Company Participants Jason Fredette - SVP, IR & Corporate Communications Martin Huber - President, CEO & Director Brian DeSchuytner - SVP, CFO & COO Conference Call Participants Jonathan Chang - Leerink Partners Colleen Kusy - Baird Ashiq Mubarack - Citigroup Boris Peaker - TD Cowen Kaveri Pohlman - BTIG Karina Rabayeva - Truist Operator Good morning, and welcome to the Mersana Therapeutics Third Quarter 20 ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-38129 Mersana Therapeutics, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation o ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-38129 Mersana Therapeutics, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation or org ...

Mersana Therapeutics, Inc. (NASDAQ:MRSN) Q1 2023 Earnings Conference Call May 9, 2023 8:00 AM ET Company Participants Jason Fredette – Senior Vice President, Investor Relations and Corporate Communications Anna Protopapas – President and Chief Executive Officer Arvin Yang – Chief Medical Officer Brian DeSchuytner – Chief Financial Officer Conference Call Participants Brian Cheng – J.P. Morgan Jonathan Chang – SVB Securities Colleen Kusy – Baird Kaveri Pohlman – BTIG Ashiq Mubarack – Citi Boris Peaker – Cowe ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2023 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number 001-38129 Mersana Therapeutics, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation or or ...

February 1, 2023 Mersana may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various factors, including, among other things, uncertainties inherent in research and development, in the initiation and advancement of clinical ...

Mersana Therapeutics, Inc. (NASDAQ:MRSN) Q4 2022 Earnings Conference Call February 28, 2023 8:00 AM ET Company Participants Jason Fredette - SVP, IR and Corporate Communications Anna Protopapas - President and CEO Arvin Yang - Chief Medical Officer Brian DeSchuytner - CFO Conference Call Participants Jonathan Chang - SVB Securities Ashiq Mubarack - Citi Asthika Goonewardene - Truist Securities Boris Peaker - Cowen Operator Good morning, and welcome to Mersana Therapeutics Fourth Quarter and Year End 2022 Co ...