Axillary Nodal Positivity in Early-Stage Invasive Lobular Carcinoma: Implications for Sentinel Lymph Node Biopsy Omission.

[BACKGROUND]  Recent trials suggest omission of sentinel lymph node biopsy (SLNB) for selected early-stage breast cancer patients. However, invasive lobular carcinoma (ILC) is underrepresented, and retrospective data indicate higher rates of nodal metastases, raising concerns about axillary understaging. This study aimed to evaluate the prevalence and predictors of nodal metastases in early-stage, clinically node-negative ILC.

[METHODS]  This study retrospectively analyzed 491 patients with estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative, clinical T1, clinically node-negative ILC who underwent breast-conserving surgery at our institution between 2004 and 2024. The exclusion criteria ruled out neoadjuvant therapy, tumor larger than 2 cm, and metastatic disease at diagnosis or prior breast cancer.

[RESULTS]  Among 491 patients, 392 (79.8 %) were pN0, whereas 99 (20.2 %) had nodal metastases (pN1mi-pN3). Pathologic tumor size was significantly associated with axillary nodal involvement (p = 0.004). In contrast, histologic subtype was not significantly associated with nodal status (p = 0.15), although pleomorphic tumors demonstrated numerically higher rates of nodal involvement than classic invasive lobular carcinoma. Menopausal status was not predictive of nodal positivity (p = 0.96).

[CONCLUSIONS]  Approximately one (20.2 %) in five patients with early-stage, clinically node-negative ILC harbors occult axillary nodal metastases. Pathologic tumor size emerged as the primary determinant of nodal involvement. Pleomorphic variants showed a tendency toward higher nodal burden. These findings indicate that omission of SLNB in ILC may carry a risk of axillary understaging with potential therapeutic implications. Pending evidence from prospective studies specifically designed for lobular histology, SLNB should continue to be considered an essential component of axillary evaluation in this subgroup.