Sentinel lymph node biopsy: strategies for pathologic examination of the specimen

Sentinel lymph node biopsy is a practical surgical procedure with high sensitivity for detection of metastases from breast carcinoma in the axilla. It offers economy by avoidance of axillary dissection in the majority of breast carcinoma patients who have negative sentinel node biopsies, and provides an opportunity to study axillary micrometastases with high efficiency in a small volume of tissue.

Sentinel node tissue is sliced at 2-mm intervals for fixation and paraffin embedding. Probabilities of finding spherical micrometastases of specific sizes randomly distributed in lymph nodes were calculated geometrically for several microsectioning plans.

Sentinel node tissue can studied by systematic serial sectioning technique designed to find metastases of given diameters with specific probabilities. A procedure whereby three microsections are prepared repeatedly at intervals of 250 microm appears to be practical. Two sections from each level can be examined by routine staining and the third by immunohistochemical stain; the latter is recommended particularly for infiltrating lobular carcinoma. This method will find metastases of 0.25-mm diameter with theoretical probability of 1, and metastases of 0.10-mm diameter with probability of 0.46, with reasonable costs. Metastases of these sizes are consequential and worth finding on biological and clinical grounds.