Does gender of offspring modify the time-related effects of a pregnancy on breast cancer risk?

Pregnancy characteristics and maternal breast cancer risk: a review of the epidemiologic literature

The short- and long-term effects of pregnancy on breast cancer risk are well documented. Insight into potential biological mechanisms for these associations may be gained by studying breast cancer risk and pregnancy characteristics (e.g., preeclampsia, twining), which may reflect hormone levels during pregnancy. To date, no review has synthesized the published literature for pregnancy characteristics and maternal breast cancer using systematic search methods. We conducted a systematic search to identify all published studies. Using PUBMED (to 31 July 2009), 42 relevant articles were identified. Several studies suggest that multiple births may be associated with a lowered breast cancer risk of about 10-30%, but results were inconsistent across 18 studies. The majority of 13 studies suggest about a 20-30% reduction in risk with preeclampsia and/or gestational hypertension. Six of seven studies reported no association for infant sex and breast cancer risk. Data are sparse and conflicting for other pregnancy characteristics such as gestational age, fetal growth, pregnancy weight gain, gestational diabetes, and placental abnormalities. The most consistent findings in a generally sparse literature are that multiple births and preeclampsia may modestly reduce breast cancer risk. Additional research is needed to elucidate associations between pregnancy characteristics, related hormonal profiles, and breast cancer risk.

Gender of offspring and maternal ovarian cancer risk

OBJECTIVE

A single live birth compared to nulliparity significantly reduces the risk for ovarian cancer, but exactly how pregnancy reduces ovarian cancer risk is unknown. We sought to determine whether offspring gender, which differentially alters maternal hormonal milieu, may be associated with maternal ovarian cancer risk.

METHODS

Parous women (n = 511) with incident ovarian cancer were compared to parous community controls (n = 1136) participating in a population-based case-control study of ovarian cancer (Delaware Valley, 1994-1998). In subgroup specific models for women with one, two, or three births, multivariate logistic regression was used to assess the relationship between ovarian cancer and offspring gender, adjusting for age, race, education, oral contraceptives, breast feeding, tubal ligation, and ovarian cancer family history.

RESULTS

Compared to having all girls, women with all boys tended to have a reduced risk of ovarian cancer (OR = 0.80 95% CI: 0.58, 1.10), while women with boys and girls conferred the greatest protection (OR = 0.58, 95% CI: 0.43, 0.79). Among women with two births, the association was observed for those with one boy and one girl (OR = 0.63, 95% CI: 0.40, 1.00), but not for those with two male offspring (OR = 1.12, 95% CI: 0.68, 1.85). This result was consistent among women with three births (OR = 0.42, 95% CI: 0.21, 0.84; OR = 0.47, 95% CI: 0.23, 0.95; OR = 0.49, 95% CI: 0.20, 1.21; for one, two, and three boys, respectively, compared to all girls).

CONCLUSION

Compared to having all girls, bearing both male and female offspring may be associated with a decrease in maternal ovarian cancer risk, although the biologic relevance of this observation is unclear.