Regeneron’s LAG-3 inhibitor fianlimab failed to beat pembrolizumab (Keytruda) in a Phase 3 melanoma trial in patients who had not received prior treatment. The combination did not improve progression-free survival by a statistically significant margin, adding to setbacks for the LAG-3 pathway. The negative readout contributed to investor disappointment after earlier expectations that the combination could produce incremental benefit over standard PD-1 therapy. The result reinforces how difficult it remains to demonstrate clear late-stage advantages for checkpoint combinations beyond single-agent PD-1 approaches.