Shares of Amgen Inc. fell 4 percent on Friday after the Thousand Oaks biotech giant said an experimental skin cancer drug had not significantly improved survival rates in clinical trial patients although it reduced the size of tumors.

The Thousand Oaks company said that the drug had met the study’s main goal of shrinking tumors. But not only were survival rates disappointing, side effects included bacterial skin infection and fever. Amgen is hoping to get initial approval of the drug to treat skin cancer that has spread to other organs.

“We remain encouraged that the study met its primary endpoint,” Dr. Sean E. Harper, Amgen’s executive vice president of research and development, said in a statement. “The strong trend in survival benefit supports further research.”

But ISI Group analyst Mark Schoenebaum told Reuters that the late-stage clinical trial results could affect the drug’s chances for Food and Drug Administration approval and limit its potential market even if approved.

Shares closed down $5.02 to $119.11 on the Nasdaq.