Clinical validation of a molecular assay for intra-operative detection of metastases in breast sentinel lymph nodes

Abstract 

Background

In breast cancer patients, the status of the sentinel lymph nodes (SLNs) has been shown to accurately reflect the presence of metastases in the axillary lymph nodes (ALNs). Intra-operative SLN evaluation by frozen section histology may miss positive cases, leading to a second surgery for complete ALN dissection. Permanent section histology itself has tissue sampling limitations and is partially dependent on pathologist expertise.

Methods

A prospective study (N=78) was conducted in our institution to validate a new intra-operative molecular assay, the GeneSearch™ breast lymph node (BLN) assay. This assay quantifies the expression of mammaglobin and cytokeratin-19 genes using quantitative RT-PCR technology to determine SLN status. Fresh SLN sections (2mm thick) were analyzed alternatively by BLN assay or post-operative histology (haematoxylin–eosin and immunohistochemistry). The subject was considered positive when histology revealed a focus >0.2mm.

Results

BLN assay results corroborated with histologic results in 75 out of 78 patients for an overall agreement of 96%, a sensitivity of 92%, and a specificity of 97%. The positive and negative predictive values of the BLN assay were of 86% (12/14) and 98% (63/64), respectively. Interestingly, a statistically significant correlation was observed between the metastases' histologic size and both assay markers' expression levels as represented by cycle time to positivity (ρ≥0.71, all p<0.0001).

Conclusions

The performance of the BLN assay in identifying nodal metastases >0.2mm was similar to that of permanent section histology, with the added advantages of an objective and rapid output that could be used for intra-operative decision to remove additional ALN.

Keywords: Real-time RT-PCR, Intra-operative sentinel lymph node biopsy, Sentinel lymph node, Breast cancer