Cytokeratin staining and other sentinel node controversies.

Sentinel lymph node (SLN) biopsy for breast cancer staging has been widely accepted because it is more sensitive and less morbid than axillary dissection. Sentinel nodes can be thoroughly scrutinized using a variety of techniques increasing the detection of micrometastases; however, the clinical relevance of micrometastases has been challenged. The available data suggest that the prognostic significance of axillary metastases is related to the size of the metastases, and the best data suggest that outcome for patients with metastases < 0.2 mm is similar to patients with node-negative disease. This would argue against the use of ultrasensitive tests such as reverse transcriptase polymerase chain reaction. Immunohistochemistry upstages 2%-20% of hematoxylin and eosin-negative sentinel nodes, and additional nodal metastases are identified in approximately 10% of completion axillary dissections prompted by an immunohistochemistry (IHC)-positive sentinel node. This would appear to be a good reason to perform IHC and act on the results. Because micrometastases can be artifactual, SLN biopsy in ductal carcinoma in situ can lead to harmful overtreatment and is best performed in the context of clinical trials. Lymphoscintigraphy has allowed the detection of alternate drainage patterns to internal mammary, infraclavicular, and supraclavicular lymph nodes. Although patients are occasionally identified who have metastases to these basins but not the axilla, this information will not impact the decision for chemotherapy in most cases. Internal mammary SLN biopsy may have value in patients with tumors < 1 cm, but requires additional evaluation in clinical trials.