Effect Modification by Time Since Blood Draw on the Association Between Circulating Fatty Acids and Prostate Cancer Risk

A recent meta-analysis suggested that circulating fatty acids do not play an important role in prostate carcinogenesis. We hypothesized that the relation between circulating fatty acids and prostate cancer (PCa) risk is modified by time between blood draw and diagnosis. We tested this hypothesis in a prospective case-control study of 476 PCa cases and matched control subjects nested in the Physicians' Health Study. The previously reported associations between fatty acids and PCa in this cohort were dramatically stronger among men diagnosed 10 or more years after blood collection. Statistically significant effect modification by time since blood collection was identified for mono-unsaturated and poly-unsaturated fatty acids and was more pronounced for aggressive tumors. Among men diagnosed fewer than 10 years since blood collection, the relative risks per interquartile range were 1.03 (95% confidence interval [CI] = 0.86 to 1.25) for total mono-unsaturated fatty acids (MUFA) and 0.95 (95% CI = 0.78 to 1.15) for total poly-unsaturated fatty acids (PUFA) whereas among men diagnosed 10 or more years after blood draw the relative risks per interquartile range were 1.69 (95% CI = 1.21 to 2.34) for MUFA (P_{heterogeneity} = .01) and 0.59 (95% CI = 0.42 to 0.83) for PUFA (P_{heterogeneity} = .02). These data suggest that the results of the meta-analysis may be partly explained by insufficient follow-up time. Furthermore, they suggest that some environmental and metabolic factors may play a role in prostate carcinogenesis decades before clinical identification of this disease.

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