Identifying Axillary Metastases in Patients with T3 Invasive Lobular Carcinoma.

Axillary lymph node (ALN) metastases are difficult to diagnose in invasive lobular carcinoma (ILC). This study evaluated the use of axillary ultrasound (AUS) and magnetic resonance imaging (MRI) in predicting ALN metastases in patients with ILC tumors >5 cm, who are at high risk of axillary metastases. This is a single-institution, institutional review board-approved, retrospective review of patients with pT3 ILC between 2014 and 2023. Clinicopathologic features, preoperative axillary imaging, surgical pathology, and locoregional or distant recurrence were collected. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. The Kruskal-Wallis (numerical covariables) and χ2 or Fisher exact (categorical covariates) tests were used with significance set at P < 0.05. In total, 139 patients with a mean age of 61 years (range 36-89) were included; all patients underwent AUS and 110 (79.1%) received preoperative MRI. After either AUS or MRI, 93 (66.9%) were classified as having clinical N0 (cN0) disease and 43 (30.9%) as cN1 disease. In total, 49.5% (46/93) cN0 patients converted to pathologic N1-3 (pN1-3) disease after surgery. A total of 43 patients had ALN fine-needle aspiration. Nine patients with negative fine-needle aspiration converted to pN1-3 disease (false negative rate of 25.7%). Despite preoperative AUS and/or MRI, nearly half of the patients with T3 ILC diagnosed as having cN0 disease converted to pN1-3. Both AUS and MRI had low sensitivity and negative predictive value. Our data suggest that current imaging has poor accuracy for axillary metastases in ILC. Surgeons should have a high index of suspicion for axillary disease, despite a negative preoperative evaluation.