Reproductive history and cutaneous malignant melanoma: a comparison between women and men.

To evaluate whether previously observed associations between parity and cutaneous malignant melanoma (CMM) risk in women reflected a biologic mechanism or resulted from uncontrolled confounding by lifestyle factors associated with parity (e.g., patterns of sun exposure), the authors investigated the effect of reproductive history (parenthood) on CMM risk in both women and men. Using information from Danish national registers (1968-2003), the authors established a population-based cohort of more than 3,500,000 persons with information on parenthood and CMM. Relative risks were estimated using Poisson regression models. Overall, number of children was significantly associated with a woman's risk of CMM (p = 0.004), with the lowest risk being seen among women with many births. Women aged 25 years or older at their first birth had a 24% (95% confidence interval: 16, 33) higher risk of CMM than younger women. Ten or more years after the birth of her youngest child, a woman had a 15% (95% confidence interval: 5, 27) higher risk of CMM than she did in the first 10 years. Similar results were observed in men. The similarity of effects for men and women suggests that lifestyle factors, rather than exposure to pregnancy hormones, may be responsible for the observed associations between reproductive history and CMM risk in women.