Mersana Therapeutics is a clinical-stage biopharmaceutical company developing antibody-drug conjugates (ADCs) for cancer. ADCs are engineered molecules that combine a targeting antibody with a cancer-killing payload, designed to deliver the payload directly to tumor cells while sparing healthy tissue. Mersana has two proprietary ADC platforms: Dolasynthen, a cytotoxic platform that uses a synthetic, site-specific scaffold to produce uniform ADCs with a precisely defined drug-to-antibody ratio; and Immunosynthen, which delivers a STING-agonist payload to activate the immune system locally within the tumor. Mersana's two clinical-stage candidates are Emi-Le, a B7-H4-targeting ADC on the Dolasynthen platform in Phase 1 trials, with an expansion cohort focused on triple-negative breast cancer patients who have already received a competing ADC class; and XMT-2056, an Immunosynthen STING-agonist ADC targeting HER2, currently in Phase 1 dose escalation. Mersana has no approved products and no commercial revenue. The company funds operations through collaboration agreements, having received upfront payments from Johnson & Johnson, Merck KGaA, and GSK for platform access, plus milestones and future royalties. GSK holds an unexercised option to exclusively license XMT-2056 globally. Mersana's near-term priorities are advancing Emi-Le toward a registration-enabling study in breast cancer and building the data package needed to trigger GSK's option on XMT-2056.