Age at Any Full-term Pregnancy and Breast Cancer Risk

Abstract

The authors analyzed data from two multistate, population-based case-control studies to investigate the association between age at any full-term pregnancy (FP) and breast cancer risk. Study subjects included breast cancer cases aged 20-79 years identified from four statewide cancer registries and randomly selected controls interviewed from 1988 to 1996. Complete information on a comprehensive set of risk factors for breast cancer was available for 9,891 cases and 12,271 controls. The large number of subjects enabled simultaneous adjustment of the covariates and efficient application of various modeling approaches. Overall, each 5-year increase in age at first FP was associated with an odds ratio of 1.07 (95% confidence interval (CI): 1.01, 1.13) for breast cancer. The corresponding estimates were odds ratio = 1.02 (95% CI: 1.00, 1.05) for age at second through ninth FPs. For age at last FP, the effect estimate (odds ratio = 1.01, 95% CI: 0.97, 1.06) was indistinguishable from that for other FPs after the first. In this analysis, a modest and transient increase in breast cancer risk after childbirth was also observed. The relatively greater effect of age at first FP is consistent with the existence of a long-term effect of early first FP on the differentiation of mammary cells, causing them to become less susceptible to carcinogenesis.

Differential effects of reproductive factors on the risk of pre- and postmenopausal breast cancer. Results from a large cohort of French women

“…The protective effect of multiparity is thus greater for cancers emerging late in life, and this agrees with recent studies that have found a transient increase in breast cancer risk immediately after each pregnancy (Lambe et al, 1994;Leon et al, 1995;Chie et al, 2000). The effect of multiparity might therefore derive from a short-term increase in risk followed by a long-term protective effect against late cancers.…”

Reproductive factors and risk of breast carcinoma in a study of white and African‐American women

“…A transient increase in breast carcinoma risk after a pregnancy has been observed in a number of studies, 17,18 but not in the CASH study, 19 and we observed no such effect in the current study as well. A potential problem associated with investigating the effects of recent pregnancy on breast carcinoma occurrence among young women is that control subjects who have experienced a recent pregnancy may be very busy and thus less willing to participate, which would result in an underestimation of recent pregnancies in the control group and an apparent increase in risk in association with such pregnancies.…”

Significant effects of mild endogenous hormonal changes in humans: considerations for low-dose testing.

“…Mild hormonal imbalance, exogenous hormonal administration (oral contraception or estrogen replacement therapy after menopause), and sheer physiologic events such as the occurrence of pregnancies or the age at first menses are involved, showing that in those cases there may be no threshold for the risk of cancer. In breast cancer, for example, epidemiologic studies (60)(61)(62) have shown that the risk is linked to different parameters integrating the lifetime duration of exposure to estrogens (i.e., age at first menses, menopause, and pregnancies). Inadequate luteal levels unable to oppose estrogen levels may also be a factor (61).…”

“…Epidemiologic studies have shown that a completed pregnancy seems to decrease the risk, whereas first-trimester interrupted pregnancies are associated with an increased risk (60). A more recent study demonstrates that the dual effect of pregnancy could be explained by the long-term protective effect against cancer and a short-term increase in risk after each pregnancy (62). In addition, it is suggested that the higher risk of postmenopausal breast cancer in obese women is linked to the aromatization of androgens into estrone in the adipose tissue (61).…”