Finasteride in prevention of prostate cancer: an important update
Posted Sep 29 2008 4:46pm
In a new analysis of the Prostate Cancer Prevention Trial (PCPT) trial data, published in Urology this month, Thompson et al. make the definitive recommendation that,
Finasteride significantly reduced prostate cancer risk regardless of the level of this risk, … this suggests that finasteride exerts both treatment and preventive effects. All men undergoing PSA screening should be informed of the potential for finasteride to reduce their risk of prostate cancer.
Finasteride clearly reduced the risk of prostate cancer by 24.8 percent in the PCPT. The goal of the most recent data analysis was to clarify whether this reduction in risk was a treatment effect or a or preventive effect, which men might be most likely to benefit from the effect.
The authors applied a relatively sophisticated statistical model (a logistic regression model) to men in the placebo group of the PCPT using risk factors for prostate cancer at entry to predict prostate cancer during the subsequent 7 years of study. Men in the two treatment groups were categorized into five groups each representing 20 percent of the participants by risk (”quintiles of risk of prostate cancer”) based on the predictive model.
A second statistical model was used to evaluate finasteride’s effect on prostate cancer for each subgroup defined by four groups each representing 25 percent of the participants by baseline PSA (”quartiles of baseline PSA”) .
The magnitude of the prevention effect of finasteride on prostate cancer was then evaluated across risk and across PSA strata, and obrained the following results:
Finasteride significantly reduced prostate cancer risk for all risk quintiles. For quintiles 1 through 5, odds ratios were 0.72, 0.52, 0.64, 0.66, and 0.71, respectively, and all results were statistically significant (P ≤ 0.05).
For quartiles of risk of entry PSA (< 0.7 ng/mL, 0.7–1.1 ng/mL, 1.1–1.7 ng/mL, and 1.8–3.0 ng/mL), odds ratios increased (smaller treatment effect) as PSA increased: 0.60, 0.62, 0.66, and 0.69, respectively, but remained significant for all strata (each P < 0.001).
The “New” Prostate Cancer InfoLink would note that there are always assumptions built into these types of statistical analysis. However, assuming that the assumptions in this analysis are reasonable, there data would appear to support the argument that finasteride offers a significant and true preventive impact on development of prostate cancer. The authors’ recommendations are likely to reignite the controversy over whether finasteride should be used much more frequently as a treatment for the prevention of prostate cancer.