Finasteride, prostate cancer, and weight gain: Evidence for genetic or environmental factors that affect cancer outcomes during finasteride treatment

OBJECTIVE: Finasteride affects both prostate cancer risk and body weight. We examined whether, during 7 years of finasteride treatment, the magnitude of weight change was associated with the diagnosis of no, low-, or high-grade cancer. METHODS: Data are from 10,057 participants in Prostate Cancer Prevention Trial (PCPT), a randomized trial of finasteride for primary prevention of prostate cancer. Mixed linear models were used to calculate percentage change in weight per year, controlling for demographic and health-related covariates. RESULTS: Weight gain was modestly lower in the finasteride compared to placebo arms (0.14 vs. 0.16% per year, P<0.025). On the placebo arm, there was no association of weight gain with cancer outcomes. In the finasteride arm, annual weight gain among men without cancer was 0.14%, and among men with cancer ranged from 0.01% for those diagnosed with high-grade cancer following a clinical indication for biopsy (P=0.03 vs. no cancer) to 0.25% among men diagnosed with low-grade cancer at the end of the trial with no indication for biopsy (P=0.002 vs. no cancer). CONCLUSIONS: In finasteride-treated men, there are significant associations between prostate cancer outcomes and weight gain, which suggest that there are common or closely related individual-level factors that affect both treatment responses. This supports the hypothesis that there are genetic characteristics and/or environmental exposures that affect finasteride outcomes which, when identified, could be used to target men most likely to benefit from finasteride treatment.