Zai Lab (HKG:9688) said a final analysis of bemarituzumab in the Fortitude-101 study found the cancer medicine was not as beneficial as previously thought, according to a Hong Kong bourse filing Wednesday.

Shares of the biopharmaceutical company, which acquired the commercialization rights for bemarituzumab for mainland China, Hong Kong, Macau, and Taiwan from US-listed Amgen, fell over 13% in morning trade Thursday.

A previous interim analysis of Fortitude-101, a phase 3 clinical trial, said bemarituzumab plus chemotherapy was superior to just chemotherapy in treating gastric cancer.

In the final analysis, however, the magnitude of the previously observed survival benefit was attenuated, Zai Lab said.

The company said it would now await results from another phase 3 trial, Fortitude-102, which is studying bemarituzumab in combination with nivolumab and chemotherapy in the same patient population.

Data readout from that trial is expected by the end of 2025 or the first half of 2026, the company said.