Extranodal extension, an international survey on its evaluation and reporting in breast cancer patients.

Lymph node metastasis is the most important prognostic factor for breast cancer patients. In addition to the number of nodes involved and the largest metastatic focus, extranodal extension (ENE) is also used to subclassify breast cancer patients into different risk groups. More recently, pathologists are required to report the size/extent of ENE per the new CAP guideline, as it seems to be associated with more axillary nodal burden and/or a worse prognosis. Although the definition of ENE is largely understood and agreed upon among pathologists around the world, evaluation and reporting for the size of ENE are not. To understand current practice, we conducted an international survey among pathologists who are interested in breast pathology. A total of 70 pathologists responded. The results showed that (1) 98% of the participants reported the presence or absence of ENE and 61% also reported the size of ENE in millimeter (mm). (2) There was no uniform method of measuring the size of ENE; 47% measured the largest dimension regardless of orientation, while 30% measured the largest perpendicular distance from the capsule. (3) The most common factors affecting the accuracy in diagnosis of ENE are the presence of lymphovascular invasion (LVI), lack of capsule integrity, and the presence of fatty hilar or fatty replacement of a lymph node. (4) 71% felt that the H&E stain is adequate to evaluate ENE, deeper levels and IHC analysis for vascular and cytokeratin markers can be helpful if needed. (5) 75% agreed that there is an urgent need to standardize the measurement and reporting for ENE. Our survey highlights the variation in ENE evaluation and the need for its standardization in breast cancer patients with axillary node metastasis.