The male predominance of the two main histologic malignancies of the small bowel cancer may reflect a role of sex hormones which will be examined in this study. This was a nationwide population-based nested case-control study, based on a cohort of subjects born between 1932 and 2008, as identified in the Swedish Multi-Generation Register. For each case of small bowel cancer, 10 age- and sex-matched controls were randomly selected. Number of children and age at having the first child were analyzed in relation to the risk of small bowel cancer using conditional logistic regression, providing odds ratios (ORs) and 95 % confidence intervals (CIs). A total of 632 female cases and 894 male cases of small bowel cancer were included. No overall increased risk of small bowel cancer was found in parous compared to non-parous women (OR = 1.02, 95 % CI 0.67-1.54). There was no association between age at first birth and small bowel cancer (> 30 years of age vs < 20 years; OR = 1.04, 95 % CI 0.72-1.50). No associations were detected in separate analyses of adenocarcinoma or carcinoid of the small bowel. No distinct risk patterns were discerned in men compared to women. Reproductive history does not seem to be associated with the risk of small bowel cancer, independent of histologic type.
