The Prostate Cancer Prevention Trial (PCPT) showed that the use of finasteride, a 5-alpha-reductase inhibitor, for 7 years reduced the risk for prostate cancer by about 25% compared with placebo.1 A new SWOG study published in the Journal of the National Cancer Institute indicates that the reduced risk for prostate cancer among men in the PCPT assigned to receive finasteride continued throughout 16 years of follow-up.2

“After the Prostate Cancer Prevention Trial a lot of questions remained, including questions about the long-term survival patterns of these patients,” explained Joseph Unger, PhD, a health services researcher at the Fred Hutchinson Cancer Research Center in Seattle, Washington. “We were interested in figuring out whether 7 years was sufficient to determine the maximum benefit of finasteride, and whether or not that benefit was maintained after 7 years.”

Previously, Dr Unger and colleagues had tried to investigate long-term survivorship of patients enrolled in a large breast cancer prevention trial by going back and trying to re-enroll women from the original investigation. However, this process was difficult and expensive, and the researchers were only able to enroll about 16% of the original patients, Dr Unger explained.

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Instead, to investigate the long-term survivorship of the PCPT, SWOG designed and managed a study that obtained a data use agreement from the Centers for Medicare & Medicaid Services (CMS) to access records from Medicare and link patients enrolled in the PCPT to their Medicare claims from 1999 through 2011.

“We were able to link 75% of the patients, which is really excellent,” Dr Unger said. “We could use those Medicare claims to figure out what these men’s long-term prostate cancer diagnoses patterns were through a median of 16 years of follow-up, adding 9 years to the 7 years on the trial.”

Overall, men in the finasteride arm of the PCPT had a 21.1% decrease in the risk for prostate cancer (HR = 1.10; 95% CI, 0.96-1.26; P < .001). The effect of finasteride was most pronounced in the first 7.5 years, which was consistent with findings from the PCPT. However, after 7.5 years, there was no increased risk for prostate cancer for men assigned to the finasteride arm.

“One concern with these kinds of interventions is that while people are taking the intervention that prostate cancer may be prevented, but then rates snap back once the intervention is discontinued,” Dr Unger said. “That did not happen here. The preventive benefit of finasteride was maintained over the 16 years.”