Survival outcomes following pregnancy or assisted reproductive technologies after breast cancer: A population-based study

Background: This study sought to determine the impact of pregnancy or assisted reproductive technologies (ART) on breast-cancer-specific survival among breast cancer survivors. Methods: The authors performed a cohort study using a novel data linkage from the California Cancer Registry, the California birth cohort, and the Society for Assisted Reproductive Technology Clinic Outcome Reporting System data sets. They performed risk-set matching in women with stages I–III breast cancer diagnosed between 2000 and 2012. For each pregnant woman, comparable women who were not pregnant at that point but were otherwise similar based on observed characteristics were matched at the time of pregnancy. After matching, Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of pregnancy with breast-cancer-specific survival. We repeated these analyses for women who received ART. Results: Among 30,021 women with breast cancer, 553 had a pregnancy and 189 attempted at least one cycle of ART. In Cox proportional hazards modeling, the pregnancy group had a higher 5-year disease-specific survival rate; 95.6% in the pregnancy group and 90.6% in the nonpregnant group (HR, 0.43; 95% CI, 0.24–0.77). In women with hormone receptor–positive cancer, we found similar results (HR, 0.43; 95% CI, 0.2–0.91). In the ART analysis, there was no difference in survival between groups; the 5-year disease-specific survival rate was 96.9% in the ART group and 94.1% in the non-ART group (HR, 0.44; 95% CI, 0.17–1.13). Conclusion: Pregnancy and ART are not associated with worse survival in women with breast cancer. Lay summary: We sought to determine the impact of pregnancy or assisted reproductive technologies (ART) among breast cancer survivors. We performed a study of 30,021 women by linking available data from California and the Society for Assisted Reproductive Technology Clinic Outcome Reporting System. For each pregnant woman, we matched at the time of pregnancy comparable women who were not pregnant at that point but were otherwise similar based on observed characteristics. We repeated these analyses for women who received ART. We found that pregnancy and ART were not associated with worse survival.