An increase in high-grade prostate cancer among men taking the drug finasteride is likely caused by an increased detection of cancers, and not by the development of more high-grade cancers, according to two studies published online September 11 in the Journal of the National Cancer Institute.
The Prostate Cancer Prevention Trial (PCPT) was the first long-term randomized trial of a possible drug to prevent prostate cancer. The trial showed a nearly 25 percent reduction in prostate cancer incidence among men who took finasteride compared with a placebo. But men taking finasteride had greater rates of high-grade prostate cancer than men taking placebo (6.4 percent vs. 5.1 percent). It is unclear whether finasteride causes more high-grade prostate cancers or simply creates a situation where more high-grade cancers are detected.
Yael Cohen, Ph.D., of Gamida Cell in Jerusalem and colleagues tested their hypothesis that finasteride reduces prostate volume and therefore increases the likelihood of finding high-grade cancer cells in a biopsy. Analyzing data from the PCPT, they investigated the association between high-grade prostate cancer and prostate volume.
Detection of high-grade cancers in the placebo group increased as the prostate size decreased. They found that prostate size in the finasteride group was 25 percent smaller than in the placebo group. Therefore, when the prostate size was taken into consideration, there was not a statistically significant difference between the prevalence of high-grade prostate cancer in the two groups.
“If our conclusion that finasteride accelerates the detection of high-grade cancer yet may not promote its development is correct, then the implications regarding the clinical impact of this drug are quite favorable. The occurrence of lower grade tumors of questionable clinical significance would be reduced, and the early detection of more serious tumors would be enhanced,” the authors write.
In a second study, M. Scott Lucia, M.D., of the University of Colorado Health Sciences Center in Denver and colleagues investigated whether finasteride changes the appearance of tumor tissue so that lower-grade tumors are diagnosed as high-grade. The researchers examined surgically-removed prostates and high-grade prostate cancer biopsies from men treated with finasteride and a placebo for signs that finasteride affected prostate size, tumor size, or disease stage.