Histopathologic examination of the sentinel lymph nodes.

Sentinel lymph nodes (SLNs) are the most likely site of regional metastasis. Their step sectioning and cytokeratin immunohistochemistry (IHC) result in the upstaging of breast cancer. The heterogeneity of histologic methods is partially responsible for differences in nodal upstaging of the disease in different reports. Intraoperative assessment might be done by both frozen sections and imprint cytology; both methods have advantages and disadvantages. Several guidelines relating to the histopathology of sentinel nodes, including the recent European Working Group for Breast Screening Pathology guidelines, are briefly summarized. These latter advocate multilevel assessment of grossly or intraoperatively negative sentinel nodes with levels separated by a maximum of 1 mm and allow IHC in their assessment, although this latter method is not mandatory. Both methods of intraoperative evaluation are allowable. There are also minimum requirements for the reports on sentinel node histology. For example, the reports should include the extent of nodal involvement, the method used for their identification, and preferably the method used for investigating the sentinel nodes, even if the results are negative. These guidelines are intended to form the basis for national guidelines in European countries.