Mersana Therapeutics (MRSN) Earnings Call Presentation

Emi-Le (XMT-1660) Clinical Development - Mersana is advancing Emi-Le to address the high unmet need in post-Topo-1 TNBC, with over 40 patients enrolled in the expansion phase at two doses and plans to present initial expansion data in the second half of 2025[5] - Confirmed objective responses were observed across various tumor types including HR+BC, endometrial cancer, ovarian cancer, and ACC-1[5] - In the intermediate dose range, an ORR of 31% (8/26) was observed in evaluable patients with B7-H4 high tumors, including a 23% (3/13) ORR in TNBC and a 50% (2/4) ORR in endometrial cancer[55] - In evaluable patients with B7-H4 high post-Topo-1 TNBC in the intermediate dose range, the confirmed ORR was 23% (3/13), and 29% (2/7) in patients with ≤4 prior lines of therapy[58] - Preliminary data in the high dose range suggest potential for even greater clinical activity, with 7 out of 11 evaluable patients achieving tumor reductions of ≥30% at doses >674 mg/m2[67] XMT-2056 and Platform Collaborations - XMT-2056, an Immunosynthen STING agonist HER2 ADC, is in Phase 1 dose escalation, with plans to present initial clinical pharmacodynamic STING activation data in 2025[5] - Mersana has a global license option agreement with GSK plc for XMT-2056[5] - Mersana has a Dolasynthen research collaboration with Johnson & Johnson and an Immunosynthen research collaboration with Merck KGaA, Darmstadt, Germany[5] Safety and Tolerability - Emi-Le was observed to be generally well-tolerated, with any treatment-related adverse event (TRAE) occurring in 830% (117/141) of patients, Grade 3 TRAEs in 369% (52/141), and TRAEs leading to treatment discontinuation in 35% (5/141)[43] - The most common TRAEs were transient AST increase, generally asymptomatic and reversible proteinuria, generally low-grade fatigue and nausea[47] Market Opportunity - The global relapsed/refractory TNBC market is projected to exceed $1 billion annually starting in 2025[28] ACC-1 Clinical Activity - In patients with ACC-1, the ORR was 556% (5/9) across all doses, unselected for B7-H4 expression[94]