Axillary Extranodal Extension in Breast Cancer: Imaging Features With Histopathology Correlation

Extranodal extension (ENE) is defined as the spread of tumor cells beyond the lymph node capsule. It is an independent prognostic factor in breast cancer associated with increased nodal disease burden, influencing subsequent treatment strategies. Extranodal extension has been reported in approximately 20% to 50% of patients with metastases to axillary lymph nodes. Despite its clinical relevance, ENE remains challenging to detect. Key imaging features indicative of ENE include irregular nodal contours, nodal matting, and perinodal edema on US and MRI. However, these findings are often not detected or are underreported. Pathologic evaluation confirms capsular permeation and perinodal soft tissue infiltration by tumor cells, which may be accompanied by a stromal response. Our case examples demonstrate the importance of integrating imaging and pathology for accurate ENE detection. Improved diagnostic accuracy with radiologic-pathologic correlation optimizes treatment planning and facilitates appropriate risk stratification for patients with breast cancer.