Reliability of whole sentinel lymph node analysis by one-step nucleic acid amplification for intraoperative diagnosis of breast cancer metastases

Objective: To assess the reliability of using the One-Step Nucleic Acid Amplification (OSNA) assay as a single test on whole sentinel lymph nodes (SLN) as a method of intraoperative diagnosis and staging of SLNs in breast cancer. Background: Combining histological and molecular assessment of metastasis on the same SLN may not fully reproduce the actual load of cancer cells present in the SLN and create problems in decisions regarding axillary dissection. Methods: Selection criteria for the whole SLN OSNA test required that the primary tumor expressed CK19 in more than 80% of tumor cells. Imprint cytology analysis of SLNs was performed together with the OSNA. Results: Of the 279 patients enrolled for SLN evaluation, 123 gave consent to the OSNA protocol and 156 to the standard histology. Thirteen patients were excluded from OSNA evaluation because of low CK19 gene expression in the primary tumor; only 2.3% were truly negative. The kappa of concordance between the imprint cytology and OSNA results was 0.52. The rate of macrometastases determined by OSNA was 11% versus 20% determined by histology, whereas the rate of OSNA-micrometastases (18%) was significantly higher than that determined by histology (8%). The rate of SLN-negative cases was similar between the 2 protocols. Macrometastases correlated with the presence of vascular invasion in both protocols. The rate of axillary lymph node metastases was consistent with SLN tumor load. Conclusions: Intraoperative OSNA assay performed on the whole SLN gave objective and reproducible results that were useful for directing decisions regarding axillary dissection and for accurately defining the SLN stage.