Sentinel Lymph Nodes in Breast Cancer: Controversies in Pathologic Evaluation Relevant to Clinical Management

Sentinel node biopsy has recently been endorsed as an acceptable alternative to axillary dissection for patients with clinically node negative breast cancer. Although outcome data from prospective trials are not yet available, observational data suggest that the technique does not increase axillary recurrence rates and may decrease morbidity. More comprehensive pathologic evaluation of sentinel nodes has contributed to enhanced detection of micrometastases and minute tumor cell clusters. The real value of the sentinel node evaluation is the ability to reliably exclude virtually all macrometastases larger than 2.0 mm. However, the mismatch between the inability to exclude minimal disease in residual unexamined tissue and the ability to detect minimal disease in microscopic sections produces tremendous heterogeneity within the micrometastasis, isolated tumor cell cluster, and node negative prognostic groups. Understanding how variation in handling sentinel nodes contributes to heterogeneity is important. Standardizing pathologic evaluation and refocusing on disease exclusion rather than minimal disease detection are critical elements in our adoption of sentinel node biopsy.