Background: Sex hormones may be associated with colorectal adenocarcinoma, although the association of pregnancy history and risk of colorectal cancer is not consistent.
Methods: We conducted a population-based nested case-control study of persons born between 1932 and 2008 who are in the Swedish Multi-Generation Register. In total, 12,915 women and 15,519 men with colorectal adenocarcinoma were identified during follow-up in the Swedish Cancer Register; 10 age- and sex-matched controls were selected for each case. Number of children and age at first and last birth were analyzed in relation to the risk of colorectal adenocarcinoma, using conditional logistic regression, to estimate odds ratios (ORs) and 95% confidence intervals (CIs).
Results: Compared with women without children, women with 1 or 2 children had an OR of 1.02 (95% CI = 0.93–1.13) of developing adenocarcinoma in the proximal colon; those with 3 or 4 children, 1.18 (1.06–1.32); and those with ≥5 children, 1.30 (1.05–1.61) (test for trend P < 0.01). The corresponding associations in men were 0.92 (0.84–1.00), 1.02 (0.92–1.13), and 0.97 (0.78–1.20), respectively (test for trend P = 0.13).
Conclusions: Higher parity in women was associated with the risk of adenocarcinoma of the proximal colon, although not the distal colon or rectum. A similar risk with family size was not seen for fathers. Still, the influence of lifestyle factors cannot be ruled out.