ASCO: Amgen's stomach cancer drug, nabbed in Five Prime buyout, extends patients' lives in phase 2

Amgen battled other biopharma suitors for Five Prime Therapeutics early this year, emerging victorious in March with a $1.9 billion deal to snap up the cancer-focused biotech. Now, the company is painting a fuller picture for bemarituzumab, the crown jewel of the buyout, showing the treatment helped patients with advanced stomach cancer live longer. 

Patients taking the treatment along with a chemotherapy combination lived a median of 19.2 months, compared to 13.5 months for the patients who took chemotherapy plus placebo. The data come from a phase 2 study Five Prime carried out in 155 patients with advanced gastric cancer or gastroesophageal junction cancer, a rare cancer of the esophagus that starts where it meets the stomach.  

Amgen is developing bemarituzumab for patients whose tumors express FGFR2b, a patient group that makes up about 30% of patients whose gastric tumors are HER2-negative. 

Stomach cancer is one of the leading causes of cancer death worldwide and—until recently—patients have suffered from a dearth of new drugs. Chemotherapy remains the standard of care for most HER2-negative patients, though, in April, the FDA approved Bristol Myers Squibb’s Opdivo as a front-line treatment for gastric cancer, gastroesophageal junction cancer and esophageal adenocarcinoma regardless of their expression of the PD-L1 marker. 

RELATED: Prime time for Five Prime as Amgen snaps up this once-moribund biotech for $1.9B and its phoenix-from-the-flames cancer asset 

Bemarituzumab did even better in a group of 96 patients (62% of the patients) who overexpressed FGFR2b in at least 10% of their tumor cells. The patients taking the bemarituzumab combo lived a median of just over two years (25.4 months) compared to 11 months for those who took chemo and placebo. 

“We were clearly very excited about that particular population—it led Five Prime to apply for and receive breakthrough designation for those patients in whom 10% or greater of their tumor cells are demonstrating FGFR2B overexpression,” said Phuong Khanh “PK” Morrow, M.D., vice president of global development at Amgen. 

But the Big Biotech is hesitant to limit bemarituzumab to that narrow group given its efficacy in the broader patient population, Morrow said. If anything, looking at the proportion of a patient’s tumor cells that overexpress the target could help Amgen and its diagnostic partners figure out which patients would benefit the most from the treatment. 

The company will meet with the FDA and other regulatory agencies to design a phase 3 study for bemarituzumab, Morrow said. That study will include a plan to monitor and prevent eye-related side effects that hit more patients taking bemarituzumab than placebo. 

RELATED: Bristol Myers' Opdivo wins landmark FDA nod as first I-O therapy for front-line stomach cancer 

Overall, side effects struck patients in both groups at roughly the same rate (100% versus 99%), but cornea-related effects afflicted more patients taking bemarituzumab than placebo (67% compared to 10%). The most common eye-related side effect was dry eye, affecting about one-quarter of patients. 

In the phase 2 study, patients were monitored for these effects, but there was no plan to prevent them from happening, Morrow said. 

“Now, we have the opportunity in the phase 3 trial to be a bit more proactive,” she said. Dry eye and other cornea-related effects took a median of six months to appear in the phase 2 study, providing a window to head them off or at least reduce their intensity, she added. 

Beyond the phase 3 study, Amgen will explore the use of bemarituzumab in other cancers. 

“FGFR2b is a receptor that is expressed across cancers that are epithelial in origin, for example, squamous non-small cell lung cancer, breast cancer, ovarian cancer, pancreatic cancer and others,” Morrow said. Non-small cell lung cancer will likely be the company's first priority after stomach cancers.