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

Abstract

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.

Preeclampsia and breast cancer: The influence of birth characteristics

“…Women with preeclampisa have in some studies been found to be characterized by having a different hormonal profile than women with normotensive pregnancies. Among these differences are lower levels of estrogens and higher levels androgens and progesterone [26]. Reduced estrogen is thought to protect against breast cancer development, and increased progesterone Table 2 Breast cancer events, person-years at risk, and incidence rate ratio (IRR) with belonging 95% confidence interval of breast cancer according to preeclampsia and birth characteristics.…”

“…Also, human chorionic gonadotropin [27] and alfa-feto protein [28] may be elevated in women with preeclampsia. Both hormones are thought to be protective against development of breast cancer by inhibiting tumor progression [27] and by acting in an antagonistic way on estrogen effects in breast tissue [26]. One study, however, showed that estrogen concentration did not differ in women with preeclampsia compared with healthy women, but found significantly higher androgen levels in women with preeclampsia [29].…”

Gestational diabetes and risk of incident primary cancer: a large historical cohort study in Israel

“…A Scottish cohort study of 753 pregnant women who underwent glucose testing at 13 weeks of pregnancy calculated a positive association between higher glucose levels and an increased risk of breast cancer diagnosed up to 20 years later [21]. An elevated risk was also observed among Israeli women with a history of GDM diagnosed with breast cancer at age 50 and above [24]. In contrast, a population-based case-control study of women first diagnosed before 35 years of age indicated an inverse association with breast cancer (OR: 0.54, 95% CI: 0.37-0.79) [44].…”

“…However, findings have been inconsistent [24], possibly due to methodological limitations such as the use of self-reported information on GDM status and relatively small study populations. The main goal of the current historical cohort study was to evaluate the risk of malignancy among women diagnosed with GDM in a large health maintenance organization (HMO) in Israel using its automated clinical databases.…”

Evaluating chemical effects on mammary gland development: A critical need in disease prevention

“…Younger age at first birth, multiple gestation pregnancies (twins and greater), preeclampsia, pre-pregnancy obesity, and gestational hypertension may all lower maternal breast cancer risk (reviewed by [33,34]), while increased placental weight [35], higher infant birth weight [34], and DES exposure during pregnancy are associated with increased risk of maternal breast cancer. One factor driving these changes is total lifetime exposure to ovarian hormones.…”