Key Takeaways
- Zymeworks (ZYME.TO/NYSE) has enrolled the first patient in its Phase 3 HERIZON-GEJ-01 trial.
- The trial evaluates zanidatamab + chemotherapy vs. standard of care in 1L HER2+ gastric/GEJ cancer.
- Phase 2 data showed 41% overall response rate and 12.5 months median PFS in heavily pre-treated patients.
- If approved, zanidatamab could address a market of approximately 85,000 patients annually in North America and Europe.
Zymeworks Inc. has initiated enrollment in its HERIZON-GEJ-01 Phase 3 trial, a pivotal study evaluating zanidatamab the company’s lead bispecific antibody in combination with chemotherapy for first-line HER2-positive gastric and gastroesophageal junction (GEJ) cancer. The trial initiation is a significant milestone for the Vancouver-based biotech, which has built its pipeline around a proprietary bispecific antibody engineering platform.
Understanding the Science
Zanidatamab is a bispecific antibody that simultaneously binds two distinct epitopes on the HER2 protein a different mechanism from standard HER2-targeting drugs like trastuzumab (Herceptin), which bind a single epitope. This dual-binding leads to enhanced HER2 clustering and receptor internalization, amplifying the anti-tumor effect. In preclinical models, zanidatamab showed synergistic activity with chemotherapy in HER2-overexpressing cancers.
| Endpoint | Phase 2 Result | Standard of Care (Historical) |
|---|---|---|
| Overall Response Rate | 41% | ~25% |
| Median PFS | 12.5 months | ~7.0 months |
| Disease Control Rate | 78% | ~60% |
| Grade 3+ Treatment-Related AEs | 34% | 30–40% (chemo-based) |
The Partnering Question
Zymeworks entered a partnership with Jazz Pharmaceuticals in 2022, with Jazz paying $325M upfront for commercial rights to zanidatamab in several indications. Jazz is co-developing the Phase 3 program and will fund the majority of costs. For Zymeworks, the arrangement provides validation and capital while retaining royalty upside a structure that has allowed the company to advance its pipeline without excessive share dilution.