Overall survival is the lowest among young women with postpartum breast cancer

Background: Women diagnosed with breast cancer prior to age 45 years (<45y) and within the first 5 years postpartum (postpartum breast cancer, PPBC) have the greatest risk for distal metastatic recurrence. Methods: Pooling data from the Colorado Young Women Breast Cancer cohort and the Breast Cancer Health Disparities Study (N = 2519 cases), we examined the association of parity, age, and clinical factors with overall survival (OS) of breast cancer over 15 years of follow-up. Results: Women with PPBC diagnosed at <45y had the lowest OS (p < 0.0001), while OS of nulliparous cases diagnosed at <45y did not differ from OS of cases diagnosed at 45-65y regardless of parity status. After adjustment for study site, race/ethnicity, clinical stage, year of diagnosis and stratification for oestrogen receptor status, PPBC remained an independent factor associated with poor OS. Among cases diagnosed at <45y, nulliparous cases had 1.6 times better OS (hazard ratio (HR) = 0.61, 95%CI 0.42–0.87) compared to those with PPBC, with a more pronounced survival difference among stage I breast cancers (HR = 0.30, 95%CI 0.11–0.79). Among very young women diagnosed at age ≤35y, nulliparous cases had 2.3 times better OS (HR = 0.44, 95%CI 0.23–0.84) compared to PPBC. Conclusion: Our results suggest that postpartum status is the main driver of poor prognosis in young women with breast cancer, with the strongest association in patients diagnosed at age ≤35y and in those with stage I disease.