MedImmune Inc. said yesterday it has ended advanced human testing of its drug Vitaxin to treat rheumatoid arthritis and psoriasis because it failed to show clinical benefits in preliminary results.

The Gaithersburg biotech firm said no safety concerns were involved and it would continue advanced testing for Vitaxin to treat melanoma and prostate cancer.

Analysts took the announcement in stride, mostly because they think the real promise for the drug is in treating cancer.

"The company has also been saying that the potential for this drug rests in cancer settings," said Eun Yang, an analyst with Wells Fargo Securities. "I don't think this is a huge disappointment at all."

Still, shares of MedImmune slipped 73 cents, or 3 percent, closing yesterday at $23.76 and helping drag down the biotech sector.

Vitaxin is an artificial antibody that targets a protein on the surface of newly forming blood vessels, as well as on certain tumors. In addition to cancer, the protein has been implicated in bone destruction in rheumatoid arthritis and the inflammatory process in psoriasis.

Jamie Lacey, MedImmune's spokeswoman, said the company "fired four shots on goal" but two didn't succeed. That doesn't raise concerns about the continuing studies because the disease processes are different, she said.

Nevertheless, analyst Yang said the announcement adds some risks to Vitaxin's development. "The fact that it didn't work in something might make people question it more," she said.

Wells Fargo maintained its hold rating on MedImmune's shares. First Albany Capital maintained its neutral rating.