EMERYVILLE, Calif. (AP) — Onyx Pharmaceuticals Inc. has reported positive clinical trial results for its cancer drug candidate, saying it worked for some multiple myeloma patients who have seen other therapies fail.

Onyx tested carfilzomib on 266 patients in the mid-stage clinical trial. Each of the patients had multiple myeloma, a cancer of the blood, and all of them had been treated with at least two previous regimens. Onyx said 36 percent of the patients saw tumors shrink, and 24 percent had at least a partial response to the drug, meaning their tumors shrank at least 30 percent.

The median response lasted 7.4 months, the company said. In premarket trading, Onyx shares climbed $2.80, or 13 percent, to $24.30.

Onyx plans to present full results from the trial at a future scientific conference. The company announced on Wednesday that it had started a late-stage trial of carfilzomib, and it plans to file for Food and Drug Administration marketing approval by the end of 2010.

The drugmaker said patients in the trial had been treated with other therapies including thalidomide and Johnson & Johnson’s drug Velcade. But the patients had experienced little tumor shrinkage, or had their tumors progress during treatment or within 60 days of the end of their most recent round of treatment.

In another recent study of carfilzomib, the most common side effects included pneumonia, anemia, and two blood disorders: neutropenia, a decrease in a type of white blood cell, and thrombocytopenia, or low levels of blood platelets, which can make clotting difficult.

Onyx gets most of its revenue from Nexavar, a kidney and liver cancer drug that is sold by Bayer HealthCare. Onyx acquired carfilzomib last year when it bought Proteolix Inc., which discovered the drug.

Nexavar is also being tested as a treatment for several other cancers.