VANCOUVER, British Columbia, June 15, 2026 – Zymeworks Inc. presented new Phase 1 clinical data for ZW191, its folate receptor alpha-targeting antibody-drug conjugate, at the ESMO Gynaecological Cancers Congress 2026, highlighting early anti-tumor activity in patients with difficult-to-treat gynecologic cancers.
The data came from the dose-escalation portion of an ongoing Phase 1 study evaluating ZW191 in patients with platinum-resistant ovarian cancer and endometrial cancer. According to the company, the treatment showed activity in tumors with both positive and negative folate receptor alpha expression, suggesting potential use across a broader patient population than some FRα-targeted approaches.
ZW191 is an antibody-drug conjugate designed to target folate receptor alpha, a protein found in many ovarian, endometrial, and lung cancers. The therapy combines a folate receptor alpha-targeting antibody with Zymeworks’ proprietary topoisomerase-1 inhibitor payload, ZD06519. The goal is to deliver the cancer-killing payload directly into tumor cells while potentially allowing bystander activity against nearby cancer cells.
Data Show Activity In Platinum-Resistant Ovarian Cancer
The latest analysis included efficacy data from Part 1 of the ongoing Phase 1 study, with a data cutoff of March 9, 2026. Folate receptor alpha expression was measured by immunohistochemistry and classified using the Proportion and Staining Intensity method.
Tumors were categorized as FRα-positive when at least 75% of cells showed 2+/3+ staining. Tumors below that threshold were classified as FRα-negative.
Among response-evaluable patients with platinum-resistant ovarian cancer, ZW191 produced a confirmed objective response rate of 78.6% in patients with FRα-positive tumors across all dose levels studied. In patients with FRα-negative tumors, the confirmed objective response rate was 47.4%.
Disease control rates were also reported across both groups. Patients with FRα-positive tumors had a disease control rate of 100%, while patients with FRα-negative tumors had a disease control rate of 89.5%.
In the overall platinum-resistant ovarian cancer population, the confirmed objective response rate was 58.8% across all dose levels. In the 6.4 mg/kg to 9.6 mg/kg dose range, the confirmed objective response rate was 65.2%.
Endometrial Cancer Cohort Also Shows Early Signal
ZW191 also showed activity in patients with endometrial cancer. In patients with FRα-negative endometrial tumors, the therapy demonstrated a confirmed objective response rate of 40% and a disease control rate of 80% across all evaluated doses.
Across the ovarian and endometrial cancer cohorts, responses were reported early and continued to deepen over time. Median duration of response had not been reached at the time of the data cutoff. Median progression-free survival across the ovarian and endometrial cancer cohorts was 7.6 months.
Zymeworks said the findings support continued development of ZW191 and may help position the therapy as a potential option for patients whose tumors have lower folate receptor alpha expression.
Safety Profile Described As Manageable
ZW191 continued to show what the company described as a manageable safety profile in the Phase 1 study.
Treatment-emergent adverse events occurred in 98% of patients. Grade 3 or higher treatment-emergent adverse events were reported in 55% of patients. The most common grade 3 or higher adverse events were neutropenia, anemia, and thrombocytopenia.
Serious treatment-emergent adverse events occurred in 35% of patients. Treatment discontinuation due to adverse events occurred in 20% of patients.
The company said the overall tolerability profile remains consistent with continued clinical development. As with all early-stage oncology studies, longer follow-up and additional trial data will be needed to better define the risk-benefit profile.
Dose Optimization Enrollment Completed
Zymeworks also reported that enrollment has been completed in Part 2a, the dose optimization portion of the Phase 1 study.
That portion of the trial is evaluating ZW191 in about 60 patients with platinum-resistant ovarian cancer. Patients were randomized to receive either 6.4 mg/kg every three weeks or 9.6 mg/kg every three weeks.
Data from Part 2a are expected to be presented at a future medical meeting. The results are expected to help guide dose selection for potential future development of ZW191.
Company Points To Broader ADC Strategy
Sabeen Mekan, M.D., Senior Vice President and Chief Medical Officer of Zymeworks, said the new findings support the differentiated profile of ZW191 and its potential role in ovarian and endometrial cancers.
The company said the response rate observed in FRα-positive ovarian cancer patients compares favorably with available therapies, while the activity in FRα-negative tumors may indicate a broader treatment opportunity.
Kosei Hasegawa, M.D., Ph.D., of Saitama Medical University International Medical Center and presenting author, also noted that the results suggest ZW191 could expand the potential benefit of FRα-targeted therapy to patients with lower folate receptor alpha expression.
What ZW191 Could Mean For Gynecologic Cancer Research
Platinum-resistant ovarian cancer remains one of the more difficult settings in gynecologic oncology. Treatment options can be limited after disease progression, and patients often need therapies that can work despite prior treatment exposure.
FRα-targeted therapies have drawn attention because folate receptor alpha is commonly expressed in several tumor types, including high-grade serous ovarian cancer and endometrial cancer. Zymeworks says ZW191 has been engineered with a novel FRα-targeting antibody, a high drug-to-antibody ratio, and the ZD06519 payload.
While the Phase 1 findings are encouraging, ZW191 remains investigational. The results come from an early-stage study, and further data will be needed to confirm efficacy, optimize dosing, assess durability, and better understand safety across larger patient groups.
About Zymeworks
Zymeworks is a global biotechnology company developing multifunctional biotherapeutics for difficult-to-treat diseases, including cancer, inflammation, and autoimmune disease. The company’s pipeline includes antibody-drug conjugates, multispecific antibody therapeutics, and other engineered biologic platforms.
ZW191 is part of the company’s broader oncology pipeline and is being studied as a potential treatment option for tumors expressing folate receptor alpha. The company is also managing licensed healthcare assets and product candidates, including Ziihera and pasritamig.
The new ESMO Gynaecological Cancers Congress 2026 data add momentum to Zymeworks’ ZW191 program, but the therapy remains in clinical development and has not yet received regulatory approval.
