Clinicopathological characteristics and prognosis of breast carcinoma with apocrine differentiation: a propensity score-matched analysis of the SEER database.

Background: Breast carcinoma with apocrine differentiation (APO) is a rare invasive cancer with unclear prognostic significance. This study compared clinicopathological features and survival outcomes between APO and invasive ductal carcinoma of no special type (IDC-NST). Methods: Data from the Surveillance, Epidemiology, and End Results (SEER) database were analyzed. Propensity score matching (PSM) was used to reduce bias. Overall survival (OS) and breast cancer-specific survival (BCSS) were assessed using Kaplan-Meier (KM) curves and Cox regression. Subgroup analyses were performed by molecular subtypes based on receptor status. Results: APO was associated with older age, higher grade, larger tumors, more lymph node involvement, higher rates of estrogen receptor (ER)/progesterone receptor (PR) negativity and human epidermal growth factor receptor 2 (HER2) positivity, and more frequent chemotherapy use (all P<0.001). Before PSM, APO exhibited worse 5-year OS (P<0.001) but similar BCSS. After PSM, APO patients demonstrated significantly better BCSS compared to IDC-NST but similar OS. Multivariate analysis identified APO as an independent favorable factor for BCSS [hazard ratio (HR) =0.672; P<0.001] and OS (HR =0.861; P=0.04). In triple-negative breast cancer (TNBC), APO independently predicted better BCSS (HR =0.72; P<0.001). No survival difference was found in HER2 positive and luminal subtypes. Conclusions: Although APO is associated with aggressive pathological features, it confers a more favorable prognosis than IDC-NST, particularly in TNBC subtype. These findings underscore the importance of molecular subtype-specific treatment strategies in the management of APO.