There is no consensus method for the histological analysis of axillary sentinel nodes (SN). This study aimed to (1) assess the rate of occult
metastases in SN using large serial sectioning and immunohistochemistry (IHC), (2) evaluate whether occult
metastases were predictive of
metastases in the downstream axillary nodes, and (3) specify a methodology of analysis of SN that could be both sensitive and applicable in daily practice. One hundred three patients with
breast carcinoma underwent SN biopsy and then axillary dissection. SN free of
tumor at standard examination of one section were sectioned at six levels (150-microm intervals) and immunostained for
cytokeratin. The number and localization of labeled metastatic cells (occult
metastases) were recorded. In 29 of the 103 patients (28%), SN were found to be metastatic after standard examination. The SN of the remaining 74 patients were further analyzed using IHC. Occult
metastases were detected in 35 of these patients (47.3%), leading to an overall SN involvement rate of 62% (29+35/103). In 33 of these 35 cases, the plurality and the dispersion of the immunostained cells implied that the screening of only 3 of the 6 levels would have led to the detection of diagnostic positive events. Only one of the 35 patients (2.8%) with occult
metastases showed metastatic lymph node in the downstream axilla. In our series of axillary SN, the analysis of one standard histologic section and, when negative, of only three additional sections after IHC revealed >60% of
metastasis or occult
metastasis.
Metastasis detected by standard analysis had a high predictive value of downstream node
metastasis, whereas the predictive value of occult
metastasis revealed by IHC was poor. The clinical significance of occult
metastases in SN needs to be specified by long-term follow-up analysis.