Pregnancy after breast cancer: A population-based study of survival and obstetric outcomes.
Authors: Rauh-Hain Jose Alejandro , Nitecki Roni , Melamed Alexander , Zubizarreta Jose , Fu Shuangshuang , Clapp Mark C. , Brady Paula C. , Kaimal Anjali J. , Giordano Sharon H. , Chavez Mac Gregor Mariana , Keating Nancy Lynn 
Published: June 2021

e18783 Background: Studies have suggested that pregnancy after breast cancer is safe, but the women who are able to conceive after cancer may also have a better prognosis. We sought to evaluate survival and obstetric outcomes among breast cancer patients in a population-based cohort. Methods: We studied women aged 18-45 years with a history of stage I-III breast cancer reported to the California Cancer Registry (CCR, 2000-2012). CCR data were linked to the 2000-2012 California Office of Statewide Health Planning and Development (OSHPD) birth cohort to ascertain both oncologic characteristics and obstetric outcomes. We compared overall survival (OS) for breast cancer patients who did or did not conceive at least 1 year after diagnosis. Breast cancer patients who conceived were matched in a 1:5 ratio to breast cancer patients who did not conceive via optimal bipartite matching accounting for follow-up time such that controls were diagnosed within a 3-month window of the cases and were alive at the time the case delivered; the distributions of cases and controls were directly balanced on socioeconomic and clinical covariates including stage, hormone receptors, and receipt of chemotherapy and radiation. For the obstetric outcomes, propensity score matching in a 1:5 ratio was used to match the same breast cancer patients who conceived to population based controls without cancer who delivered during the study years. Wald statistics, conditional Cox proportional hazards model, and conditional logistic regressions were used to evaluate outcomes. Results: We matched 417 patients aged 18-45 years at time of breast cancer diagnosis who conceived at least one year following diagnosis with 2,085 breast cancer patients who did not conceive. All covariates were balanced within 0.1 mean standardized difference. The majority of the cohort was non-Hispanic White (51%), with stage II disease (53%). The 5-year overall survival for cases relative to controls was 97.6% and 95.7% respectively. There was no difference in overall survival between patients who conceived and those who did not conceive following treatment for breast cancer (HR 0.58, 95% CI 0.3-1.1). Breast cancer patients did not have higher risks of preterm birth before 37 weeks (odds ratio [OR] 0.91, 95% CI 0.39-2.14), small-for-gestational age birthweight ( < 10th percentile: OR 0.93, 95% CI 0.67-1.29; < 5th percentile: OR 0.67, 95% CI 0.39-1.14), cesarean delivery (OR 1.12, 95% CI 0.92-1.35), severe maternal morbidity (OR 1.14, 95% CI 0.61-2.12), or neonatal morbidity (OR 1.08, 95% CI 0.77-1.53) relative to controls. Conclusions: In a population-based cohort, breast cancer patients who conceived at least 1 year after diagnosis did not have worse OS than matched breast cancer patients who did not conceive. Breast cancer patients who conceived during the study period did not have an increased risk of adverse obstetric outcomes compared to population-based controls without cancer.