Immunotherapy drugs that fight cancer have been touted as the biggest growth driver in biotech, but the field suffered a major setback Friday when Incyte announced that its trial drug epacadostat did not slow disease progression for melanoma patients and that the study would halt. Incyte’s stock dropped 23% Friday, wiping $4 billion off its market capitalization. The failure of the drug, which now seems unlikely to work for most other kinds of cancer patients, raises concerns about the current wave of immunotherapy combination trials. Biotech research is currently overrun with drug combinations aiming to boost the efficacy of two competing blockbuster drugs, Merck’s Keytruda and Bristol-Myers Squibb’s Opdivo, and Incyte’s drug was among the most promising of the bunch, with some of the best preliminary data. The silver lining for the field is that the drug worked in a very different way than most other combinations under development.