Evaluation of one-step nucleic acid (OSNA) molecular assay for intra-operative diagnosis of sentinel lymph node metastasis

194 Background: One step nucleic acid (OSNA) is a recently developed molecular diagnostic assay to detect lymph node metastases. Aim of the present study was to assess OSNA for intra-operative detection of sentinel node metastases with use of standard histopathology as the “gold standard.” Moreover, discordant cases were further investigated to assess their impact on patients’ management. Methods: 157 breast cancer patients with clinically and ultrasonographically negative axilla underwent axillary staging with sentinel node (SLN) biopsy. 244 SLNs were evaluated by OSNA and standard histopathology (alternate slices were submitted to OSNA and standard test). The “turn-around time” taken for an intra-operative OSNA result was recorded. Results: Sensitivity and specificity of OSNA were 92.3% and 95.6% respectively with positive predictive value of 80% and negative predictive value of 98.4%. The average time taken for an intra-operative result in this group was 34 minutes. Concordance rate was 95% while 12/244 nodes showed discordant results between OSNA and Histology. The discordant cases were re-evaluated by histopathologists and characteristics of this subgroup analysed. Patient’s management was altered by OSNA alone in 5 patients as they underwent axillary lymph node dissection on the basis of a positive OSNA when histopathology did not show evidence of metastasis. Two patients with nodes negative on OSNA had histopathology results showing metastases requiring delayed axillary clearance. The rest of the discordant nodes belonged to patients who had other nodes biopsied concurrently that were concordant in OSNA and histology. Conclusions: OSNA is a fast, valuable and highly accurate standardised method for the intra-operative evaluation of axillary lymph node metastasis and is part of our routine intra-operative assessment tool for sentinel nodes in breast cancer.