Pregnancy vs. Postpartum Breast Cancer: Distinct Tumor Biology and Survival Trends in a Contemporary Cohort.

Background: Pregnancy-associated breast cancer (PABC), defined as breast cancer diagnosed during pregnancy or within one year postpartum, is a unique and clinically challenging entity. Evidence suggests that tumors diagnosed during pregnancy (PrBC) and postpartum (PPBC) may differ in biology and prognosis. This study compares clinical features, treatment patterns and outcomes between PrBC and PPBC. Methods: We performed a retrospective analysis of 76 women diagnosed with PABC from January 2000 to June 2023 across two tertiary centers. Patients were classified according to ESMO guidelines as PrBC (n = 41) or PPBC (n = 35). Clinical presentation, tumor characteristics, treatment approaches and survival outcomes were evaluated. Overall survival (OS) and disease-free survival (DFS) were estimated using Kaplan-Meier analysis and compared with log-rank tests. Results: A total of 76 patients with PABC were included (41 PrBC, 35 PPBC; median age 37 years). Most tumors were high-grade invasive ductal carcinomas, with Luminal B predominant in PrBC and triple-negative breast cancer (TNBC) in PPBC. Locally advanced disease was common (axillary involvement 52%; de novo metastases 9%). Surgery was performed in most cases, with breast conservative surgery (BCS) more frequent in PrBC and mastectomy in PPBC; 46% received neoadjuvant chemotherapy. At median follow-up of 68 months, 7.9% of patients had died and 29% experienced recurrence. Oncologic outcomes were similar between subgroups, with a trend in favor of PrBC. Pregnancy continuation did not adversely affect outcomes. Conclusions: PrBC and PPBC display heterogeneous clinical presentations with a trend toward more favorable outcomes in PrBC. These findings support the need for tailored counseling, individualized management and research designs that differentiate between PrBC and PPBC.