Reproductive factors, exogenous hormones, and pancreatic cancer risk in the CTS

Female steroid hormones are hypothesized to play a protective role in pancreatic cancer risk. However, results from epidemiologic studies that examined hormone-related exposures have been inconsistent. The California Teachers Study is a cohort study of female public school professionals that was established in 1995-1996. Of the 118,164 eligible study participants, 323 women were diagnosed with incident invasive pancreatic cancer through December 31, 2009. Multivariable Cox proportional hazards regression methods were used to estimate hazard ratios and 95% confidence intervals for the association of pancreatic cancer risk with reproductive factors and exogenous hormone use. Current users of estrogen-only therapy at baseline (1995-1996) had a lower risk of pancreatic cancer than did participants who had never used hormone therapy (hazard ratio = 0.59, 95% confidence interval: 0.42, 0.84). Use of estrogen-plus-progestin therapy was not associated with the risk of pancreatic cancer. A longer duration of oral contraceptive use (≥10 years of use compared with never use) was associated with an increased risk of cancer (hazard ratio = 1.72, 95% confidence interval: 1.19, 2.49). Reproductive factors, including age at menarche, parity, breastfeeding, and age at menopause, were not associated with pancreatic cancer risk. Our results suggest that increased estrogen exposure through estrogen-only therapy may reduce pancreatic cancer risk in women.