Mortality of Pregnancy Following Breast Cancer Diagnoses in Taiwanese Women

BACKGROUND: This work examined the association between pregnancy after breast cancer (BC) diagnosis and total mortality in Taiwanese patients with BC. MATERIALS AND METHODS: The Taiwan Cancer Registry, National Health Insurance database, and Taiwan National Death Certificate database were reviewed. Patients who became pregnant after being diagnosed with BC were selected (n = 249). Four nonpregnant patients with BC were selected and matched to every pregnant patient with BC by age at diagnosis, year at diagnosis, and propensity score based on disease stage, tumor size, node involvement, and histological grade. The disease‐free time interval for the selected control needed to have been longer than the time interval between the cancer diagnosis and pregnancy for the index case. Follow‐up was calculated from the pregnancy date of the index case to the date of death or December 31, 2014, whichever came first. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: After adjusting for age, year at BC diagnosis, stage, positive nodes, and hormone therapy, patients with BC who became pregnant after their cancer diagnosis had lower total mortality than did the comparison group (HR = 0.44, 95% CI = 0.23–0.84), including that of estrogen receptor‐positive patients (HR = 0.23, 95% CI = 0.07–0.77). The inverse association was more pronounced for those who became pregnant more than 3 years after diagnosis (HR = 0.19, 95% CI = 0.05–0.78). CONCLUSION: Our nationwide retrospective analysis revealed that pregnancy after BC diagnosis was associated with lower mortality than that of nonpregnant patients with BC at a similar age, year at diagnosis, and clinical characteristics. IMPLICATIONS FOR PRACTICE: This article provides high‐level evidence based on an Asian population for pregnancy counseling after a breast cancer diagnosis, including for patients with estrogen receptor‐positive cancers. The study also revealed the optimal time for patients who would like to become pregnant after breast cancer.