NIAGARA FALLS, ONTARIO—Finasteride use decreases the risk of prostate cancer (PCa) without significantly increasing the risk of either high-grade or lethal prostate cancer (PCa), according to an analysis of data from the Health Professionals Follow-up Study (HPFS).

Lead investigator Mark Preston, MD, a urologist at Massachusetts General Hospital in Boston, presented study findings at Canadian Urological Association’s 68th Annual Meeting. He and his colleagues conducted the study after the FDA issued a notice to healthcare professionals in June 2011 stating they believed men being treated with 5-alpha reductase inhibitors (5-ARIs) for benign prostatic hyperplasia (BPH) were at increased risk of developing high-grade PCa. FDA also instructed manufacturers of these medications to revise the product labels to include this information.

The FDA based its conclusions on the results of two large, randomized, controlled trials. The Prostate Cancer Prevention Trial (PCPT) compared finasteride 5 mg per day to placebo for seven years in BPH patients. The Reduction by Dutasteride of Prostate Cancer Events (REDUCE) compared dutasteride 0.5 mg per day to placebo for four years. The FDA determined there was a reduction in overall PCa risk in patients on active treatment in the two trials. However, they found that this was largely due to a reduced incidence of lower-risk forms of PCa and there was an increased incidence of high-grade prostate cancer with 5-ARI treatment.

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“This sparked our investigation into this important question of the effects of 5-ARIs on the incidence of metastatic or fatal prostate cancer using a large, well-established prospective cohort,” Dr. Preston said.

The HPFS has been following male health professionals since 1986. The subjects were 40 to 75 years of age at the start of the study. The investigators focused on the information collected from 38,430 cancer-free men every two years starting in 1996 and ending in 2010. They were all cancer-free in 1996.

PCa developed in 3,710 men. Of these, 293 were lethal cases, 578 were advanced cases, and 463 were high-grade. The remaining or 72% of the individuals had local PCa. Furthermore, 2,920 of the men had used finasteride – which is indicated for treatment of BPH at some time between 1986 and 2010. After adjusting for confounders, men who had ever used finasteride had a 23% reduced risk of any PCa and a 34% decreased risk of Gleason 7 disease.

Commenting on the new findings, Curtis Nickel, MD, Professor of Urology at Queen’s University in Kingston, Ont., said the apparent higher rate of high-grade PCa detected in the finasteride (PCPT) and dutasteride (REDUCE) PCa prevention trials in patients randomized to the 5-ARI did not appear be due to causation but rather to a number of biases, such as change in PSA, reduction in prostate volume, and suppression of low-grade cancers.

“The 5-alpha reductase inhibitors finasteride and dutasteride do not make high-risk prostate cancer,” said Dr. Nickel, who was not involved in the new study. “Rather, they appear to suppress both BPH and low-grade low-risk cancer, and like the scum that rises out of the muck, we more easily detect the higher-grade, higher-risk prostate cancer—in other words, the potentially lethal cancer that we want to find.”