Cancer
Adverse Pregnancy Outcomes and Subsequent Risk of Breast Cancer among Postmenopausal Women Godness BIney* Godness Biney Su Yon Jung Angela M. Malek Michelle J. Naughton Lihong QI Peter Schnatz Cassandra Spracken
Epidemiological evidence suggests that pregnancy offers some level of protection against breast cancer possibly due to changes in hormonal profiles that result in a more differentiated and less susceptible mammary gland, or changes within specific epithelial cell subpopulations. However, the extent to which pregnancy offers protection if it ends in an adverse outcome (e.g., preeclampsia and preterm birth) remains uncertain. This study aimed to examine the association between adverse pregnancy outcomes, including preeclampsia, gestational hypertension, gestational diabetes, preterm birth, low birth weight and high birth, and the subsequent risk of breast cancer. The WHI is a large, multi-racial cohort of postmenopausal women in the US. At baseline, women were first asked to report if they had ever been pregnant. Participants were later asked during follow up to report the outcomes of their pregnancies whether any of their pregnancies resulted in adverse outcomes, including preeclampsia, gestational hypertension, gestational diabetes, preterm birth, low birth weight and high birth weight. Based on the information collected at baseline and follow-up (Extension II), we created an all-adverse pregnancy variable (Yes/No) to collectively assess the relationship with the outcome. Incident breast cancers were all adjudicated and binary in nature (Yes/No). Cox proportional hazard regression models were used to estimate the unadjusted and adjusted hazard ratios (HR) and their 95% confidence intervals (95% CI) for the association between adverse pregnancy outcomes and incident breast cancer. After adjusting for crucial covariates (e.g., age at first birth, family history of breast and ovarian cancer, race/ethnicity, etc.), we found that women with any adverse pregnancy outcomes were at slightly decreased risk of developing breast cancer (HR: 0.92 (95% CI : 0.84 – 0.99)) compared to their counterparts without adverse pregnancy outcomes. Our results indicates that pregnancy regardless of its adverse outcome may still offer some level of protection against breast cancer.