Impact of Axillary Burden on Survival: A Comparative Study of Invasive Lobular Carcinoma and Invasive Ductal Carcinoma in Early-Stage Breast Cancer.

Objective: Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the most common breast cancer types. While they differ biologically and pathologically, their association with axillary lymph node (ALN) metastasis and survival remains unclear. This study compares the clinical features of ILC and IDC to evaluate ALN surgery considerations for ILC patients.

Methods: We retrospectively analyzed 3543 patients who underwent upfront surgery for early breast cancer at Yonsei University Severance Hospital between January 2015 and December 2019. Multivariate logistic regression assessed factors linked to ALN metastasis, while Cox regression identified predictors of recurrence and survival.

Results: Among the patients, 92.1% had IDC and 7.9% had ILC. T2-stage tumors were more prevalent in ILC (31.4% vs. 18.1%, p < 0.001). The rates of ALN metastasis were similar between the groups (IDC: 21.1%, ILC: 24.6%, p = 0.655); however, the presence of more than two metastatic ALNs was more frequent in ILC (9.6% vs. 5.0%, p = 0.004). Factors associated with having >2 metastatic ALNs included histology, suspicious axillary ultrasound, T stage, and lymphovascular invasion. The median follow-up period was 65 months, with no significant differences observed in 8-year recurrence-free survival (ILC: 95.2%, IDC: 94.1%, p = 0.134) or 5-year overall survival (ILC: 97.1%, IDC: 97.4%, p = 0.289).

Conclusions: ILC features larger tumors and a higher nodal burden but has similar survival rates to IDC with proper treatment. Caution is essential in axillary surgery to avoid underestimating the nodal burden.