Reproductive factors and pancreatic cancer risk: a Norwegian cohort study.

A cohort of 63,090 Norwegian women born 1886-1928 was followed more than 38 years, and relations between reproductive factors and risk of pancreatic cancer were explored; 449 cases were recorded at ages 50-89 years. Age at menopause showed a moderately positive association with risk (rate ratio (RR)=1.08 per 2 years delay in menopause; 95% confidence interval (CI)=1.00-1.17). Neither parity nor duration of breastfeeding showed significant associations with risk after adjusting only for demographic factors. With mutual adjustment, however, parity became positively associated (RR=1.13 per delivery; 95% CI=1.05-1.22) while duration of breastfeeding was inversely associated (RR=0.87 per 12 months; 95% CI=0.78-0.97). These associations lessened in magnitude with increasing age, and were essentially absent above age 80 years. Risk was raised among women reporting at least one abortion, but no trend was seen with number of abortions. Together with previous studies, the findings raise questions about the role of chance, but do not exclude hormonal factors related to breastfeeding and pregnancy from affecting pancreatic cancer risk.