Long-term safety of pregnancy following breast cancer according to estrogen receptor status

Safety of pregnancy in women with history of estrogen receptor (ER)–positive breast cancer remains controversial. In this multicenter case–control study, 333 patients with pregnancy after breast cancer were matched (1:3) to 874 nonpregnant patients of similar characteristics, adjusting for guaranteed time bias. Survival estimates were calculated using the Kaplan-Meier analysis; groups were compared with the log-rank test. All reported P values were two-sided. At a median follow-up of 7.2 years after pregnancy, no difference in disease-free survival was observed between pregnant and nonpregnant patients with ER-positive (hazard ratio [HR] ¼ 0.94, 95% confidence interval [CI] ¼ 0.70 to 1.26, P ¼ .68) or ER-negative (HR ¼ 0.75, 95% CI ¼ 0.53 to 1.06, P ¼ .10) disease. No overall survival (OS) difference was observed in ER-positive patients (HR ¼ 0.84, 95% CI ¼ 0.60 to 1.18, P ¼ .32); ER-negative patients in the pregnant cohort had better OS (HR ¼ 0.57, 95% CI ¼ 0.36 to 0.90, P ¼ .01). Abortion, time to pregnancy, breastfeeding, and type of adjuvant therapy had no impact on patients’ outcomes. This study provides reassuring evidence on the long-term safety of pregnancy in breast cancer survivors, including those with ER-positive disease.