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

Invasive lobular carcinoma (ILC) is the second most common histological type of breast cancer. Despite its distinct clinical and pathological characteristics, ILC shares the same prognostic classification system and adjuvant treatment strategies as invasive ductal carcinoma (IDC). We reviewed the data of the 16,365 IDC and ILC patients who were treated between 2005 and 2022 at Seoul National University Hospital (SNUH). Also, we conducted a parallel analysis using the data of 247,290 IDC and ILC treated between 2010 and 2015 from the surveillance, epidemiology, and end results (SEER) database. ILC patients were older at diagnosis, had larger tumors, and ILC tumors were predominantly HR-positive/HER2-negative. ILC exhibited unique prognostic implications of anatomic features. Unlike in IDC, the tumor size and nodal status showed differential prognostic impact on survival in ILC. While there was no significant survival difference for different T stages in ILC patients, the prognostic impact of nodal involvement was more pronounced for ILC in the SNUH dataset. Similar survival implication of tumor size and nodal involvement was observed for the ILC cases in the SEER dataset. In ILC, tumor size may not be as strong a predictor of survival as in IDC, while advanced nodal involvement carries a particularly high risk for breast cancer-specific mortality.