- ZW191 demonstrates compelling anti-tumor activity in heavily pretreated patients with platinum-resistant ovarian cancer across folate receptor alpha (FRα) expression levels
- Confirmed objective response rates (cORR) of 64.5% at the 6.4 mg/kg dose in patients with high-grade serous platinum-resistant ovarian cancer
- Median duration of response not yet reached at either dose level at median 7 months follow-up, with six-month progression-free survival rate of 61% in both groups
- Favorable tolerability profile, particularly at 6.4 mg/kg, supports continued clinical development in partnership or through a strategic collaboration
- Conference call with Zymeworks management on October 27 at 8:30 am Eastern Time (ET)
VANCOUVER, British Columbia, Oct. 24, 2026 (GLOBE NEWSWIRE) -- Zymeworks Inc. (Nasdaq: ZYME), a biotechnology company managing a portfolio of licensed healthcare assets while developing a diverse pipeline of novel, multifunctional biotherapeutics, today presented new clinical data from the randomized dose-optimization portion of its ongoing Phase 1 study evaluating ZW191, a FRα-targeting antibody-drug conjugate (ADC), at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain.
The presentation highlights compelling anti-tumor activity in heavily pretreated patients with platinum-resistant ovarian cancer (PROC), including patients with high-grade serous disease across all levels of FRα expression. The results demonstrate compelling response rates, durability and a favorable tolerability profile, particularly at the 6.4 mg/kg dose, further supporting the potential of ZW191 to address limitations of currently available FRα-targeted therapies and expand treatment opportunities for patients with ovarian cancer.
“We are highly encouraged by these results, which further demonstrate the differentiated clinical profile of ZW191 and its potential to deliver meaningful benefit to patients with platinum-resistant ovarian cancer,” said Sabeen Mekan, M.D., Senior Vice President and Chief Medical Officer, Zymeworks. “The robust response rates observed at both doses, including meaningful activity in patients with low or negative FRα expression, reinforce the potential of ZW191 to benefit a broader patient population. Importantly, the encouraging durability of responses and favorable tolerability profile, particularly at 6.4 mg/kg, provide valuable insights to guide dose selection and the next stage of clinical development.”
The analysis included efficacy and safety data from 80 patients with PROC randomized to receive ZW191 at 6.4 mg/kg (n=37) or 9.6 mg/kg (n=43) every three weeks, as of the September 10, 2026 data cutoff date. Patients were heavily pretreated, having received a median of four prior lines of therapy, with 45% receiving five or more prior lines. Median follow-up was seven months. FRα expression was assessed by immunohistochemistry and categorized as low/negative (0%–24%), intermediate (25%–74%) or high (75%–100%) based on the percentage of tumor cells with 2+ or 3+ staining intensity.
Key Findings
Among response-evaluable patients with high-grade serous PROC, ZW191 demonstrated a cORR of 64.5% at 6.4 mg/kg and 55.3% at 9.6 mg/kg, with disease control rates of 100% and 92.1%, respectively. These findings demonstrate compelling anti-tumor activity at both doses in a heavily pretreated patient population.
ZW191 demonstrated meaningful anti-tumor activity across FRα expression in patients with high-grade serous PROC. Confirmed objective response rates were 69.2% in patients with high FRα expression, 50.0% in patients with intermediate FRα expression and 55.0% in patients with low or negative FRα expression. These findings support the potential of ZW191 to show improved efficacy than existing FRα targeted therapies in FRα high population and meaningfully benefit patients with lower expression who may not be eligible for currently approved FRα targeting therapies.
Responses to ZW191 were deep and durable, with median duration of response not yet reached at either dose. Six-month progression-free survival (PFS) was 61% in both groups, while median PFS was 7.9 months at 6.4 mg/kg and 9.8 months at 9.6 mg/kg in patients with high-grade serous PROC. At the time of data cutoff, 45% of patients remained on treatment, and PFS data continue to mature, especially at 6.4 mg/kg.
ZW191 continued to demonstrate a favorable tolerability profile, particularly at 6.4 mg/kg. Grade 3 or higher treatment-related adverse events occurred in 22% of patients receiving 6.4 mg/kg compared with 44% at 9.6 mg/kg. Treatment-emergent adverse events leading to dose reductions occurred in 5% and 33% of patients, respectively, while discontinuations due to adverse events occurred in 14% and 19%. No deaths due to treatment-emergent adverse events were reported in either treatment group. The overall safety profile was manageable and supports continued clinical development.
“These results are particularly promising for patients with platinum-resistant ovarian cancer who have exhausted available treatment options,” said Jung-Yun Lee, M.D., Ph.D., Yonsei Cancer Center and Severance Hospital, Seoul, Republic of South Korea, and primary investigator who presented the results at ESMO 2026. “We observed substantial anti-tumor activity in patients who had received multiple prior therapies, including meaningful responses across high, intermediate and low or negative FRα expression levels. The encouraging durability of responses, together with the favorable safety profile observed at the lower dose, suggests ZW191 has the potential to become an important new treatment option for patients with this difficult-to-treat disease.”
The findings demonstrate encouraging anti-tumor activity across the 6.4 mg/kg and 9.6 mg/kg dose levels, with a more favorable tolerability profile at 6.4 mg/kg. These results will inform optimal dose selection for further clinical development.
ZW191's differentiated profile, including its novel FRα-targeting antibody, proprietary topoisomerase I inhibitor payload, ZD06519, and high drug-to-antibody ratio, supports its potential to address key limitations of existing therapies and broaden the applicability of FRα-targeted treatment approaches.
The presentation will be available on Zymeworks’ website at www.zymeworks.com/publications/.
Investor Call Details
Zymeworks invites investors and the general public to view and listen to a live webcast of its conference call with investment analysts at 8:30 am ET on October 27, 2026.
Dial-in details and webcast link are available on Zymeworks’ website at https://ir.zymeworks.com/events-and-presentations. A webcast replay of the call will be available on the Zymeworks website within 24 hours following the conclusion of the live call and will be archived for a limited period.
About ZW191
ZW191 is an antibody-drug conjugate engineered to target a protein called folate receptor-⍺ found in ~75% of high-grade serous ovarian carcinomas,1 over 50% of endometrial cancers,2,3 and ~70% of lung adenocarcinomas4. ZW191’s differentiated design strongly supports its ability to internalize into FR⍺-expressing cells with the potential to release bystander active topoisomerase-1 inhibitor (ZD06519), a novel proprietary payload developed by Zymeworks to kill tumor cells.
The Company has engaged MTS Healthcare to evaluate strategic partnering opportunities to fund further development for ZW191 with the objective of maximizing long-term value.
About Zymeworks Inc.
Zymeworks is a global biotechnology company building a diversified portfolio of healthcare assets designed to generate durable cash flows while advancing innovative medicines for difficult-to-treat diseases. The Company’s asset and royalty aggregation strategy combines a growing portfolio of commercial and near-commercial assets, including YUPELRI® (revefenacin), with a differentiated internal research and development engine. Zymeworks’ portfolio also includes Ziihera® (zanidatamab-hrii), a HER2-targeted bispecific antibody discovered and developed by Zymeworks and commercialized through global partnerships with Jazz Pharmaceuticals and BeOne Medicines, and pasritamig, a clinical-stage multispecific antibody developed by Johnson & Johnson using Zymeworks’ proprietary antibody engineering technologies.
Zymeworks is advancing a diverse pipeline of novel biotherapeutics, leveraging its proprietary Azymetric™ platform and expertise in antibody-drug conjugates, multispecific antibodies and other next-generation antibody technologies. These capabilities, together with Zymeworks’ integrated drug development expertise, enable the Company to develop differentiated therapeutics and create value through both internal innovation and strategic partnerships.
