Key Findings
At the ESMO Congress 2026, Zymeworks reported that ZW191 achieved a confirmed objective response rate (cORR) of 64.5% at the 6.4 mg/kg dose and 55.3% at the 9.6 mg/kg dose in patients with high-grade serous PROC. Disease control rates were 100% and 92.1%, respectively. Notably, the drug showed activity regardless of FRα expression levels: cORR was 69.2% in high expression, 50.0% in intermediate expression, and 55.0% in low or negative expression patients.
Technical Details
The randomized dose-optimization study included 80 heavily pretreated PROC patients (median of four prior lines of therapy; 45% receiving five or more). Patients were randomized to receive ZW191 at either 6.4 mg/kg (n=37) or 9.6 mg/kg (n=43) every three weeks. FRα expression was categorized via immunohistochemistry as low/negative (0%–24%), intermediate (25%–74%), or high (75%–100%).
Regarding durability, the median duration of response was not yet reached at either dose level at a median follow-up of seven months. The six-month progression-free survival (PFS) rate was 61% for both groups, with median PFS reaching 7.9 months at 6.4 mg/kg and 9.8 months at 9.6 mg/kg in high-grade serous PROC patients.
Safety and Tolerability
The 6.4 mg/kg dose exhibited a more favorable safety profile. Grade 3 or higher treatment-related adverse events occurred in 22% of patients at 6.4 mg/kg, compared to 44% at 9.6 mg/kg. Dose reductions due to treatment-emergent adverse events were reported in 5% of the 6.4 mg/kg group and 33% of the 9.6 mg/kg group. Discontinuations due to adverse events were 14% and 19%, respectively. No treatment-related deaths were reported.
Significance and Outlook
The data indicates that ZW191 may address limitations of current FRα-targeted therapies by providing meaningful benefit to patients with lower FRα expression who are typically ineligible for existing treatments. Zymeworks intends to use these results to guide dose selection for the next stage of clinical development, potentially through a strategic collaboration or partnership.
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