WASHINGTON (AP) – Early trials of a new drug for advanced prostate cancer are showing some success, researchers report.

Of the first 30 patients treated with MDV3100, 13 showed declines of more than 50 percent in the levels of chemicals in the blood that indicate the presence of the cancer.

However, the tests are only in phase 1 and 2, where drugs are checked for safety, side effects and early indications of effectiveness. The drug still faces a larger phase 3 tests of effectiveness before it can be proposed for use.

The preliminary findings, by a team led by Charles L. Sawyers of Memorial Sloan-Kettering Cancer Center in New York, are reported in tomorrow's edition of the journal Science.

The treatment is for prostate cancer that has metastasized, or spread to other areas of the body.

Men with these cancers are often treated with drugs that inhibit the activity of male hormones, which can drive tumour growth. But tumors can become resistant to those drugs.