ORLANDO (Reuters Health) - Treatment for 1 year with a low daily dose of toremifene, an agent used to treat advanced breast cancer, significantly reduces the risk that prostatic intraepithelial neoplasia (PIN) will develop into prostate cancer, according to new study findings.

"With this study, we demonstrate that PIN patients are truly at risk for prostate cancer and that one in three with PIN will go on to develop prostate cancer," Dr. David Price of Regional Urology, LLC in Shreveport, Louisiana told participants here at the 41st annual meeting of the American Society of Clinical Oncology.

This study also shows that toremifene 20 mg daily for 1 year leads to "a dramatic 48% reduction in the incidence of prostate cancer in men with high-grade PIN," he said.

Dr. Price explained that both testosterone and estrogen have been implicated in the development of prostate cancer and to-date testosterone has been the target of most chemoprevention trials in prostate cancer. Toremifene was selected for this trial over tamoxifen because it is more selective for the estrogen receptor alpha, which is thought to play a role in prostate carcinogenesis.

In the study, 514 men with high-grade PIN and no evidence of prostate cancer at entry were randomly assigned to toremifene (20 mg, 40 mg, or 60 mg once daily) or placebo for 1 year. All of the men were underwent repeat biopsy at 6 and 12 months.

Of 447 patients available for evaluation, prostate cancer was diagnosed among significantly fewer patients taking toremifene 20 mg compared with patients taking placebo (24.4% versus 31.2%) based on 6- and 12-month biopsy data (p < 0.05).

For men with no evidence of prostate cancer on the 6-month biopsy who completed the entire 1-year treatment period, the incidence of prostate cancer was reduced by 48% with toremifene 20 mg.

For the men who received 40 mg and 60 mg toremifene daily for 1 year the incidence of prostate cancer was also lower compared with placebo but not statistically significantly so.

Intention-to-treat analyses show that toremifene 20 mg daily prevents 6.8 prostate cancers per 100 PIN patients treated per year. "This compares favorably with other cancer prevention trials," Dr. Price said, noting that in a breast cancer prevention trial using tamoxifen, "there were 0.7 cancers prevented per 100 patients per year, so this is approximately a 10-fold difference."

Toremifene was "safe and very well tolerated" with the incidence of serious adverse events with toremifene roughly equivalent to that of placebo, which is important for a chemopreventive agent, Dr. Price noted.

This is the first drug to show promise for lowering the incidence of prostate cancer in men with high-grade PIN, the researcher noted. He warned, however, that more trials are needed before toremifene can be widely recommended for men with high-grade PIN.

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