Differential prognostic significance of tumor size and lymph node in invasive lobular carcinoma of breast 

Abstract Despite invasive lobular carcinoma (ILC) having distinct clinical and pathological characteristics, it shares the same prognostication system and adjuvant treatment strategies with invasive ductal carcinoma (IDC). We analyzed data from 16,410 IDC and ILC patients treated at Seoul National University Hospital (2005–2022), along with 247,290 cases from the Surveillance, Epidemiology, and End Results (SEER) database (2010–2015). ILC patients were characterized by older age at diagnosis, larger tumors, and predominantly HR-positive/HER2-negative status. ILC showed unique prognostic implications, particularly in anatomic features. Unlike IDC, tumor size and nodal status had differential prognostic impact on survival in ILC. While T stages showed no significant survival difference in ILC patients, nodal involvement had a more pronounced prognostic impact in both SNUH and SEER datasets. These findings suggest that in ILC, tumor size may not be as strong a survival predictor as in IDC, while advanced nodal involvement indicates higher breast cancer-specific mortality risk.