Boston ? Full results of a big study testing a drug for preventing prostate cancer show a higher risk of heart failure, a surprise finding that could dampen enthusiasm for expanding its use.

On Monday, GlaxoSmithKline PLC asked the federal Food and Drug Administration to approve its drug Avodart as a cancer preventive for men at higher-than-normal risk of the disease. The drug is already sold for urinary problems, and no heart failure risks have been seen with that use, doctors say.

Results of a study testing it as a cancer preventive were given at a medical conference last year, but the heart risk information had not been analyzed at that time so only the main results of the study were presented, a Glaxo spokeswoman said. Full results are being published in today’s New England Journal of Medicine.