Shares of Incyte Corp. INCY, -1.08% plunged 19% in premarket trade Friday, and Merck & Co. Inc.'s stock MRK, -0.02% dropped 1.9%, after the companies said an external data monitoring committee (eDMC) determined that results from a phase 3 study evaluating Incyte's epacadostat with Merck's Keytruda in patients with metastatic melanoma did not meet the primary endpoint of improving progression-free survival. Incyte's stock had been halted until 8 a.m. ET for news. The companies said the second primary endpoint of overall survival was also not expected to reach statistical significance. The companies said they decided to stop the study based on the eDMC's recommendation. "While we are disappointed that this study did not confirm the efficacy of epacadostat in combination with KEYTRUDA in patients with unresectable or metastatic melanoma, data from ECHO-301/KEYNOTE-252, including analyses of an extensive biomarker panel, will contribute to our understanding of the role of IDO1 inhibition in combination with PD-1 antagonists, and may inform our broader epacadostat clinical development program," said Incyte's Chief Medical Officer Steven Stein. Incyte's stock had shed 16.8% over the past three months through Thursday, while Merck shares had lost 4.3% and the Dow Jones Industrial Average DJIA, +0.99% had slipped 3.1%.