Background: The role of progestogens in colorectal cancer development is poorly characterized. To address this, our group developed a highly sensitive assay to measure concentrations of seven markers of endogenous progestogen metabolism among postmenopausal women. Methods: The markers were measured in baseline serum collected from postmenopausal women in a case-cohort study within the breast and bone follow-up to the fracture intervention trial (B~FIT). We followed women not using exogenous hormones at baseline (1992-1993) for up to 12 years: 187 women with incident colorectal cancer diagnosed during follow-up and a subcohort of 495 women selected on strata of age and clinical center. We used adjusted Cox regression models with robust variance to estimate risk for colorectal cancer [hazard ratios (HR), 95% confidence intervals (CI)]. Results: High concentrations of pregnenolone and progesterone were not associated with colorectal cancer [quintile(Q)5 versus Q1: pregnenolone HR, 0.71, 95% CI, 0.40-1.25; progesterone HR, 1.25; 95% CI, 0.71-2.22]. A trend of increasing risk was suggested, but statistically imprecise across quintiles of 17-hydroxypregnenolone (Q2 to Q5 HRs, 0.75-1.44; Ptrend, 0.06). Conclusions: We used sensitive and reliable assays to measure multiple circulating markers of progestogen metabolism. Progestogens were generally unassociated with colorectal cancer risk in postmenopausal women. Impact: Our findings are consistent with most prior research on circulating endogenous sex hormones, which taken together suggest that sex hormones may not be major drivers of colorectal carcinogenesis in postmenopausal women.
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