Amgen's bemarituzumab trial has taken a turn, with a final analysis showing weaker survival benefits than previously found in an earlier pre-specified interim analysis.
In June, Amgen and China partner Zai Labs reported that monoclonal antibody bemarituzumab plus chemotherapy provided a clinical and statistically significant improvement in overall survival for certain gastric cancer patients in the Fortitude-101 trial. That was at the pre-specified interim analysis, which served as the study’s primary analysis.
Now, the completed final analysis shows that “the magnitude of the previously observed survival benefit has attenuated,” Zai Labs said in a brief press release. The company did not share the data driving the statement.
Zai Labs holds co-development and commercialization rights for the drug candidate in greater China and had previously been racing toward regulatory submission in the country based on the interim analysis. The Zai-sponsored study specifically assessed bemarituzumab in those with locally advanced or metastatic gastric or gastroesophageal junction cancer that were non-HER2 positive and had an overexpression of fibroblast growth factor receptor 2b (FGFR2b).
With the less positive outcome of the final analysis, Zai is left to wait on a different study that looks at bemarituzumab plus chemotherapy and Bristol Myers Squibb’s Opdivo before making any regulatory filings. That trial, called Fortitude-102, studies the same population and is scheduled for a data readout by the end of 2025 or the first half of 2026, according to Zai.
William Blair analysts had already been “cautious” evaluating bemarituzumab, according to a Sept. 3 note to clients. The analysts noted the importance of the upcoming Fortitude-102 readout given that Opdivo and chemotherapy is the standard of care in the proposed indication, and also cited known safety issues.
Ocular toxicity safety concerns that had been observed in a phase 2 trial occurred with greater frequency and severity in the late-stage study, the companies had disclosed at the interim analysis. Zai Lab’s thin update on the final analysis did not mention any safety findings, but Amgen will present the results from the interim and final analysis at an upcoming medical meeting.
Despite their caution, analysts with William Blair said it was “disappointing to see the survival benefit deteriorate with additional follow-up,” especially since a regulatory filing seems to place “full reliance” on positive data from the ongoing Opdivo study.
It's likely now that William Blair’s previous expectation of a 2026 commercial launch and $480 million in 2030 sales will be edited to wait on the pending results. Even so, bemarituzumab has a “limited market opportunity” and thus likely wouldn't be a major value driver for Amgen.
The company had picked up the phase 3-ready candidate in a $1.9 billion acquisition of Five Prime Therapeutics back in 2021. Bemarituzumab holds breakthrough therapy status from the FDA for gastric cancer patients with at least 10% of cells overexpressing FGFR2b.