Surgical pathology of lymph nodes in cancer staging: routine and specialized techniques

In conclusion, routine and specialized techniques available to the pathologist for evaluating regional lymph nodes for evidence of metastatic malignancy have been presented. A variety of methods are available for increasing the number of lymph nodes identified, more thoroughly sampling the identified nodes either by gross or microscopic serial sectioning, and applying immunohistochemistry and other techniques to improve the sensitivity of detecting malignant cells. In the end, standard practice regarding the application of these techniques must be dictated by the demonstrated clinical usefulness of the information obtained, and tempered by the realities of cost and workload constraints on diagnostic pathology laboratories. In interpreting studies addressing prognostic significance of micrometastases, the definition of the term micrometastases, biologic behavior of tumors in different sites, and of tumors of different cell types from the same site (e.g., lobular versus ductal carcinoma of the breast) must be considered. Evaluating the evidence to date suggests that there may be a lower limit to the size of nodal metastases that portends an adverse prognosis. The commonly accepted definition of micrometastases as those less than 2 mm may have to be qualified as the meaning of metastases of varying sizes becomes clearer for specific subsets of patients with different tumor types. The existence of circulating tumor cells in a variety of malignancies is known but of uncertain significance in individual cases. It cannot be predicted whether sparse tumor cells found in lymph nodes are destined for immune destruction or tumor progression. For the present, it appears that careful gross sectioning and microscopic evaluation using well-accepted routine techniques will identify the vast majority of clinically significant lymph node metastases. The place of IHC and other ancillary techniques in the routine evaluation of regional lymph nodes in pathologic cancer staging remains to be determined.