Shares of Incyte Corp., the Wilmington-based drug developer, fell 22.9 percent Friday, to $64.02 a share, after the company and Merck said a trial of Incyte's "powerful" immunosuppressant drug, epacadostat, combined with Merck's cancer-fighting drug Keytruda, failed to keep alive skin-cancer patients any longer than giving them plain Keytruda.

Incyte is one of the largest among a group of firms trying to develop cancer treatments based on the protein Indoleamine 2,3-dioxygenase (IDO2), which inhibits cell reproduction. Shares of another IDO-focused company, Iowa-based NewLinks Genetics, fell 42.6 percent to $4.20 per share. Incyte, which last year completed a new headquarters for hundreds of workers on the site of the former Wanamakers store near the US 202 exit from I-95, has other drug-development deals with Merck rival Bristol-Myers Squibb, Roche, and AstraZeneca.

"Based on these results," and the recommendations of the independent data-monitoring committee overseeing the tests, "the study will be stopped," the companies said in a joint statement.  "While we are disappointed," analysis of the tests on metastatic melanoma patients — in a study dubbed Echo-301/Keynote-252 — "will contribute to our understanding" and future immunosuppressant therapies, Incyte chief medical officer Steven Stein said in a statement.

"We look forward to sharing the comprehensive data analysis from ECHO-301/KEYNOTE-252 with the scientific community at an upcoming medical meeting," added Merck Laboratories chief medical officer Roy Baynes.