Zymeworks Announces ZW191 Anti-Tumor Study Results

Zymeworks announced results from the dose-escalation part of the Phase 1 study for ZW191, a folate receptor alpha, or FRalpha,-targeting antibody-drug conjugate, or ADC, at the 2026 American Association for Cancer Research, or AACR, Annual Meeting. The data from Part 1 of the ongoing global Phase 1 study highlight a compelling combination of anti-tumor activity and manageable safety in patients with advanced, heavily pretreated solid tumors, including ovarian and endometrial cancers. Part 2a, the dose-optimization portion of the study evaluating patients with ovarian cancer at doses of 6.4 mg/kg and 9.6 mg/kg, has completed enrollment, with participants recruited globally across North America, Europe, and Asia-Pacific. The data from Part 2a will determine the recommended dose for any future registration studies. In platinum resistant ovarian cancer patients, ZW191 demonstrated a cORR of 56% across all dose levels, with tumor regression observed in 68% of patients and disease control achieved in 94%. Notably, ZW191 demonstrated compelling anti-tumor activity in the 6.4-9.6 mg/kg dose range regardless of FRalpha expression, with a cORR of 61% observed in ovarian and 57% in endometrial cancers, with disease control observed in 100% of patients. These findings highlight the potential for ZW191 to benefit a broad patient population, including those with low or heterogeneous target expression. In endometrial cancer, ZW191 showed a cORR of 40% across all dose levels and 57% in the 6.4-9.6 mg/kg cohort, with disease control rates of 80% and 86%, respectively. Responses were observed regardless of FRalpha expression levels, suggesting potential activity across a broad patient population. Across ovarian and endometrial cancer cohorts, responses were observed early, with a median time to response of 1.4 months. ZW191 was well tolerated and safely administered up to 11.2 mg/kg.