Mersana Therapeutics (MRSN) TD Cowen 45th Annual Healthcare Conference summary

Strategic focus and innovation

• Emphasizes the need to improve on existing ADC platforms by developing novel scaffold linker payloads to address dose-limiting toxicities and cross-resistance issues.

• Highlights a unique opportunity in the post-Topo ADC space, as competitors have withdrawn or shown no activity in this setting.

• Introduces a novel STING payload for selective tumor delivery, with initial pharmacodynamic data expected this year.

• Fast track designation underscores the high unmet need in post-Topo patients, expanding the potential market.

• Platform’s differentiated safety profile enables potential for combination therapies, including with platinum and TROP2 ADCs.

Clinical data and program updates

• Emily (XMT-1660), a B7-H4 ADC, shows a 23% confirmed response rate in B7H4-high TNBC post-Topo patients, with expansion into earlier lines underway.

• Safety profile includes transient AST increase, low-grade nausea, fatigue, and reversible proteinuria, with no grade 4/5 treatment-related adverse events.

• Protocol amendments now allow dose reduction and treatment through proteinuria, aiming to improve confirmed response rates at higher doses.

• Ongoing dose expansion and backfill at higher doses, with data updates and a second high-dose cohort planned for this year.

• Enrollment is strong, aided by competitor withdrawal and investigator enthusiasm.

Competitive landscape and market potential

• Only program with demonstrated activity in post-Topo TNBC, as other ADCs with Topo payloads show no efficacy in this setting.

• Pfizer’s discontinuation and other competitors’ challenges in post-Topo recruitment create a unique market position.

• Trodelvy’s global TNBC sales benchmark at $1B, with HR-positive breast cancer representing a market five times larger.

• Fast track status and biomarker-driven approach position the program for regulatory and commercial advantage.

• Potential for expansion into gynecologic oncology and earlier lines of therapy through combination regimens.