Men who drink heavily may be raising their risk of developing prostate cancer, researchers reported Monday.

What's more, their study found, the drug finasteride, which can help lower a man's risk of the disease, appears unable to undo the damage of heavy drinking.

The findings come from a clinical trial of nearly 11,000 men looking at whether finasteride lowered the risk of prostate cancer over seven years. Of the men, 2,219 were diagnosed with prostate cancer, and 8,791 remained cancer-free throughout the study.

The researchers found that men who drank heavily — four or more drinks per day, on at least five days out of the week — were twice as likely as non-drinkers to develop aggressive prostate tumors.

The risk was seen in both men who received finasteride and those given a placebo.

In addition, when it came to less aggressive, slower-growing prostate tumors, finasteride cut non-drinkers' and moderate drinkers' risk by 43 percent. The drug did nothing, however, for heavier drinkers.

Researchers led by Dr. Zhihong Gong, of the University of California at San Francisco, report the findings in the journal Cancer.

Many of the established risk factors for prostate cancer cannot be controlled, such as older age, African-American race and family history of the disease. Only a handful of suspected risk factors — including obesity, smoking and a high intake of animal fat — can be modified, Gong's team notes.

Heavy drinking may need to be added to that short list, the researchers say, though they also point out that more studies should be done to confirm the findings.

For now, they write, "physicians may choose to consider this finding when counseling men on reducing their risk of prostate cancer."

It would also be "prudent," they add, for men on finasteride to limit themselves to no more than two or three drinks per day.