Diagnostic Axillary US: How Indication and Breast Cancer Status Impact Diagnostic Outcomes

To determine how indication and breast cancer status impact the observed prevalence of lymph node (LN) metastases, axillary US (AxUS) performance indices, and sonographic presentation of metastatic LNs.

In total, 2156 consecutive AxUS examinations in 1719 women >18 years old from May 22, 2017, to December 10, 2020, were identified. Indication, breast cancer status, and imaging results were obtained. Lymph node status was established ≥1 year follow-up. Axillary US examinations were reviewed, blinded to clinical and pathology outcomes. Axillary US performance indices were compared by cancer status using an unpaired proportion test. Lymph node characteristics between breast cancer statuses were assessed using logistic regression analysis.

Observed LN metastases prevalence in the overall study population was 1.7% (23/1340). In all, 62.2% (1340/2156) of AxUS examinations were performed in women without breast cancer; "Treatment planning" made up only 5% (108/2156) and had the highest prevalence-24.1% (26/108). Lymph node metastases prevalence was between 0% and 0.7% for all indications in women without breast cancer other than AxUS prompted by another imaging modality. "Follow-up" and "routine" axillary evaluation during diagnostic breast US had a combined prevalence of 0.20% (1/504). Metastatic LNs in women without current/suspected breast cancer had larger cortices and were more likely to have an absent hilum and abnormal shape.

This study highlights the need to incorporate examination indication and cancer status during AxUS interpretation, particularly in women without current or suspected breast cancer. It is also important to be cognizant of observed differences in sonographic features of LN metastasis based on breast cancer status.