Is axillary imaging for invasive lobular carcinoma accurate in determining clinical node staging?

Preoperative evaluation of clinical N-stage (cN) is difficult in breast cancer patients with invasive lobular carcinoma (ILC). Our goal was to assess the predictive value of axillary imaging in ILC by comparing imaging cN and pathologic N-stage (pN).

A single-institution retrospective review was performed for newly diagnosed stage I-III ILC patients undergoing preoperative breast imaging from 2011 to 2016. Clinicopathologic factors; mammogram, MRI, and ultrasound findings; and surgical pathology data were reviewed. Sub-analysis for pN2-N3 patients was performed to determine imaging sensitivity for patients with a larger nodal disease burden. Statistical analysis included sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of each imaging modality.

Of the total 349 patients included, 70.5% were cN0, and 62% were pN0 (p = 0.03). For all patients, mammogram sensitivity was 7%, specificity 97%, PPV 50%, NPV 72%; ultrasound sensitivity was 26%, specificity 86%, PPV 52%, NPV 67%; MRI sensitivity was 7%, specificity 98%, PPV 80%, NPV 51%. For pN2/N3 patients, 38% were identified as cN0. Mammogram sensitivity was 10%; ultrasound 42%; MRI 65%. Pathology evaluation of N2/N3 patients indicated LN were replaced with ILC but maintained normal architecture. The average largest pathologic tumor deposit (1.5 ± 0.8 cm) correlated with average largest imaging LN size (1.4 ± 0.6 cm) (p = 0.58).

A statistically significant difference between clinical and pathologic N-stage exists for ILC patients. MRI was most sensitive for identification of pN2-N3 patients and should be considered part of routine axillary imaging evaluation for ILC patients.