Histological examination of sentinel lymph nodes: significance of macrometastasis, micrometastasis, and isolated tumor cells

Abstract

Sentinel lymph node biopsy has been started in 1990s and has become one of the standard diagnostic procedures used to treat patients with early breast cancer in this century. In Japan, for the microscopic diagnosis of metastasis to sentinel lymph nodes, intraoperative frozen section diagnosis is widely used in combination with subsequent permanent section diagnosis of the residual specimens. Metastatic foci to sentinel lymph nodes have been classified into macrometastasis, micrometastasis, and isolated tumor cells in 2002, and the definition of isolated tumor cells was modified in 2010. Clinical significance of occult sentinel lymph node metastases, being mostly composed of micrometastasis and isolated tumor cells, has been clarified in terms of predictive factors for non-sentinel lymph node metastasis and patient prognosis by large-scale retrospective studies and prospective randomized clinical trials. In the present review, clinical implications of micrometastases and isolated tumor cells in sentinel lymph nodes and the methods for pathological examination of SLN metastases employed in these studies were overviewed.