Background/Objectives: Pregnancy-associated breast cancer (PABC) is uncommon but increasingly encountered as more women delay childbearing. Its prognostic impact remains controversial, particularly for cancers diagnosed in the early postpartum period. We aimed to synthesize contemporary evidence on the prognosis of breast cancer diagnosed during pregnancy or within 12 months after delivery compared with breast cancer in other young women, with a specific focus on differences between pregnancy time and postpartum disease. Methods: We performed a systematic review of observational studies published from 2005 onwards that reported oncologic outcomes for women with invasive PABC versus non-PABC comparators or PABC-only cohorts with internal timing comparisons. PubMed, Cochrane Library, Scopus and ClinicalTrials.gov were systematically searched using predefined strategies. Two reviewers independently screened records, extracted data and assessed risk of bias using the ROBINS-E tool, treating PABC status as the exposure. Because of substantial heterogeneity in PABC definitions, outcomes and adjustment sets, no meta-analysis was performed. Results: Twenty-one observational studies (single-center, multicenter and population-based) were included. PABC cases more often presented with larger tumors, higher nodal burden, high-grade and hormone receptor-negative/HER2-positive phenotypes and worse survival compared to non-PABC controls. In most contemporary cohorts that delivered guideline-oriented therapy and adjusted for stage and tumor biology, a diagnosis during pregnancy was not an independent predictor of poorer disease-free or overall survival. In contrast, multiple large registry and institutional studies reported significantly higher risks of recurrence and death for cancers diagnosed in the early postpartum period, even after multivariable adjustment. Conclusions: Current evidence suggests that pregnancy itself does not inevitably worsen breast cancer prognosis when treatment is not compromised. However, breast cancers diagnosed soon after childbirth represent a distinct high-risk subgroup. These findings support full-intensity, guideline-based therapy during pregnancy and highlight the need for special attention and further research focused on postpartum breast cancer.
Zouzoulas et al. (Tue,) studied this question.