Finasteride use results in a significantly lower risk of prostate cancer (PCa) long after the medication is discontinued, researchers concluded.

The finding extends the results of the Prostate Cancer Prevention Trial (PCPT), which demonstrated that 7 years of finasteride treatment decreased the risk of PCa by 25% compared with placebo among men aged 55 years and older. Whether this risk-lowering effect of finasteride is maintained after discontinuing the drug has been unclear.

To examine PCa risk beyond the 7-year study period, Joseph M. Unger, PhD, MS, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues linked PCPT study records to subjects’ Medicare claims data. The linkage enabled PCa to be identified by both clinical records and Medicare claims. The median follow-up was 16 years. Overall, finasteride recipients had a 21.1% decreased risk of PCa compared with placebo recipients, Dr Unger’s team reported online in the Journal of the National Cancer Institute.

The beneficial effect was most pronounced in the first 7.5 years (29% reduction in PCa risk), consistent with original PCPT findings, Dr Unger’s team reported. After 7.5 years, the investigators observed no increased risk of PCa among finasteride recipients.

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In the PCPT, investigators randomly assigned 18,880 men to receive finasteride or placebo daily for 7 years. To be eligible for the study, men had to be aged 55 years or older with normal findings on digital rectal examinations and PSA levels of 3.0 ng/mL or less. In the current study, 14,176 participants (75.1%) had a linkage to Medicare claims (7069 in the finasteride arm and 7107 in the placebo arm), although all 18,880 men were included in the analysis.

“The use of Medicare claims data to augment follow-up for PCPT participants illustrates how the use of secondary data sources can enhance the ability to detect outcomes over the long term from prospective studies,” the authors noted.

Reference

Unger JM, Hershman DL, Till C, et al. Using Medicare claims to examine long-term prostate cancer risk of finasteride in the Prostate Cancer Prevention Trial. J Natl Cancer Inst. 2018; DOI: 10.1093/jnci/djy035