Scientists have discovered the first drug that promises to prevent prostate cancer, but deciding who should use it won't be easy because it may actually trigger aggressive tumor growth in some men who do develop the disease. The drug is already sold as a treatment for enlarged prostates under the brand name Proscar and, in a much lower dose, as Propecia for baldness. Men who took Proscar daily for seven years cut their chances of getting prostate cancer by nearly 25% compared with men given a dummy pill, researchers reported Tuesday in the New England Journal of Medicine. The results were strong enough that the study of 18,000 men age 55 and older, originally scheduled to run for another year, was stopped this month. "This trial proves prostate cancer, at least in part, is preventable," said Peter Greenwald, cancer prevention chief at the National Cancer Institute, who participated in the study himself and so far is cancer-free. "It's a huge step forward."
Proscar works by preventing testosterone from changing into another hormone that fuels prostate enlargement and cancer growth. In the study, it worked equally well for men at low risk of cancer, and those at high risk--African-American men and those whose fathers and brothers had the disease. But some troubling findings have critics questioning just how often Proscar should be used. Men who developed prostate cancer while taking Proscar were more likely to have high-grade, aggressive tumors--6.4% of Proscar users were diagnosed with aggressive tumors, compared with 5.1% of men given a placebo. Impotence and loss of libido are also common side effects of the medication, particularly among older men.
Nearly 220,900 U.S. men each year are diagnosed with prostate cancer. It is the second most common cancer among men after skin malignancies. An estimated 28,900 American men will die from prostate cancer in 2003.