Pathology issues related to SN procedures and increased detection of micrometastases and isolated tumor cells

The goal for the pathologist when dealing with sentinel nodes (SNs) of breast cancer patients is not to find all metastases, but to find clinically relevant metastases: those associated with further metastases beyond the SN, necessitating further locoregional treatment, or indicating an adverse prognosis, necessitating adjuvant systemic therapy. Pathology examination of the SN has to be done more with more attention than usual and can be done pre-operatively, post-operatively, but also intra-operatively to allow immediate axillary lymph node dissection when necessary. There are several means for pre-operative, intra-operative and post-operative SN pathological evaluation. These include fine needle aspiration cytology, gross examination, imprint cytology, frozen section analysis, histopathological investigation by step sectioning, immunohistochemistry, and molecular analysis. In this paper, we provide an up to date discussion on the virtues and flaws of these different methods to find SN metastases, and provide recommendations on the optimal pathology protocol for breast cancer SNs.