Prognosis and associations between reproductive factors and molecular subtypes in Chinese women with pregnancy-associated and non-pregnancy-associated breast cancer: a retrospective cohort study

Pregnancy-associated breast cancer (PABC) presents unique clinical challenges. However, its clinicopathological characteristics and prognosis compared with non-PABC, as well as the associations between reproductive factors and molecular subtypes, remain incompletely understood. This single-center retrospective cohort study included 382 consecutive eligible women with stage I–III breast cancer, comprising 185 PABC and 197 non-PABC patients. Associations between reproductive factors and molecular subtypes were evaluated using multinomial logistic regression. Recurrence-free survival (RFS) was examined using Kaplan–Meier estimates and Cox proportional hazards models. After 1:1 propensity score matching (PSM), 129 patients were included in each group. PABC patients had higher histological grades, more advanced T stage, and a higher proportion of triple-negative breast cancer (TNBC; 18.9% vs. 8.1%). Within PABC, birth interval < 5 years was associated with higher odds of TNBC versus luminal subtype (adjusted OR 3.15, 95% CI 1.15–8.64), whereas lactation for 1–<2 versus ≥ 2 years was inversely associated with TNBC (adjusted OR 0.22, 95% CI 0.08–0.64). Exploratory analyses suggested associations of shorter birth interval and lactation duration with TNBC among PABC patients, although neither association remained significant after FDR correction. PABC was associated with poorer RFS in the full cohort (adjusted HR 3.27, 95% CI 1.28–8.40) and matched cohort (adjusted HR 3.64, 95% CI 1.08–12.31). Birth interval was not significantly associated with RFS within PABC. These findings suggest that reproductive factors may be associated with the molecular heterogeneity of PABC, and this observation should be confirmed in larger prospective cohorts.