But screening is expected to become less common because a government advisory committee, the United States Preventive Services Task Force, has recommended against routine screening, saying that more men are harmed by unnecessary treatments for prostate cancer than are saved from death by screening. That could lead to an increase in men whose initial diagnosis is metastatic cancer, Dr. Vogelzang said.

The study, sponsored by the National Cancer Institute, involved 790 men who received either only hormone therapy or hormone therapy in addition to at most six infusions of docetaxel spaced three weeks apart.

Those who received the chemotherapy lived a median of 57.6 months, compared with 44.0 months in the control group, a difference of 13.6 months. The difference in survival was even greater — 17 months — for the patients whose cancer had spread more extensively. Dr. Morris of Sloan-Kettering said those men were the best candidates for early chemotherapy.

Docetaxel is sold under the brand name Taxotere by Sanofi, but generic versions are also available. It was approved for metastatic prostate cancer in 2004. In the last few years, several other drugs have been approved, like Zytiga from Johnson & Johnson and Xtandi from Medivation and Astellas Pharma.

But docetaxel and the newer drugs are typically used after hormone therapy has stopped working. In that setting, each of them has extended median survival by about two to five months in clinical trials.

Dr. Matthew R. Cooperberg, associate professor of urology at the University of California, San Francisco, said doctors were starting to use the newer agents before docetaxel, pushing chemotherapy further back in the sequence.

So the new study “is, to an extent, bucking the tide,” he said. “This trial may be evidence that the role for chemo is earlier, when patients are healthier and the disease burden is relatively low.”