Can preoperative axillary US help exclude N2 and N3 metastatic breast cancer?

PURPOSE: To determine the false-negative rate of axillary ultrasonography (US) with respect to stage N2 and N3 metastatic disease in patients with newly diagnosed breast cancer.
MATERIALS AND METHODS: The study was approved by the institutional review board and complied with the HIPAA; the requirement for informed consent was waived. A retrospective search of radiology records identified 435 consecutive patients with breast cancer aged 25-88 years who underwent preoperative axillary US from January 1, 2006, to December 31, 2007. Two hundred five patients (203 women and two men) had 208 negative US scans with correlative surgical and/or pathologic lymph node data. Criteria used to detect abnormal lymph nodes included subjective assessment of diffuse cortical thickening, focal cortical mass/thickening, and replacement or effacement of the fatty hilum. Tumor type, grade, size, and hormone receptor status were documented. Statistical analysis was performed with the Fisher exact test.
RESULTS: Of the 208 axillae with negative findings at US, 14 (6.7%) had a final node stage of N2 or N3. Twelve of the 208 axillae (5.8%) had stage N2 disease and two (1.0%) had stage N3 disease. Of the 14 axillae with stage N2 or N3 disease, eight (57.1%) had lobular histologic characteristics and six (42.9%) had ductal histologic characteristics. The false-negative rate for N2 and N3 disease was 4.1% (six of 146 axillae) for invasive ductal cancer and 17% (eight of 47 axillae) for invasive lobular cancer (P < .01). None of the 14 axillae with stage N2 or N3 disease were "triple negative" (ie, estrogen receptor negative, progesterone receptor negative, and human epidermal growth factor receptor type 2 negative).
CONCLUSION: Preoperative axillary US excluded 96% of N2 and N3 invasive ductal metastases. The false-negative rate for N2 and N3 invasive lobular cancer was significantly higher than that for invasive ductal cancer, which suggests that axillary US cannot be used to exclude N2 and N3 metastases in these patients. © RSNA, 2010.