Regeneron's Fianlimab Combo Falls Short of Proving Superiority Over Merck's Keytruda

Regeneron's experimental drug combination failed to prove superior to Merck's Keytruda in treating melanoma, according to a late-stage trial. The company tested its fianlimab drug combined with Libtayo against Keytruda and found that while the fianlimab arm showed a numerical improvement in progression-free survival, the difference was not statistically significant.

The trial, which was published on May 15, 2026, compared the combination of fianlimab and Libtayo to Keytruda alone in patients with advanced melanoma. In the high-dose arm, patients lived a median of 11.5 months without their cancer worsening, compared to 6.4 months for those on Keytruda alone.

Regeneron is continuing a separate late-stage trial comparing the same combination against Bristol Myers Squibb's Opdualag. The company said that full results from the current trial will be presented at a future medical meeting.

The setback is a disappointment for Regeneron as it tries to carve out a position in the fast-growing melanoma immunotherapy market. Fianlimab plus Libtayo remains an investigational therapy with no approved indication yet.