Multicenter study evaluating the clinical performance of the OSNA assay for the molecular detection of lymph node metastases in gastric cancer patients

Background: The accurate diagnosis of lymph node (LN) metastasis is important for making treatment decisions for gastric cancer patients. This multicenter study evaluated the clinical performance of the one-step nucleic acid amplification (OSNA) assay (Sysmex Corp.), an automated system that detects cytokeratin 19 (CK19) mRNA, in detecting LN metastases in gastric cancer patients. Methods: LNs retrieved from patients who had undergone gastric cancer surgery at one of the four Japanese hospitals involved in this study were divided into blocks at 2-mm intervals. Alternate blocks were examined with the OSNA assay and the remaining blocks were assessed histologically. Results: A total of 394 LNs from 61 patients were examined. The concordance rate between the OSNA assay and the histological examination was 0.942 (95 % CI, 0.914-0.963). Sensitivity and specificity of the OSNA assay compared to the histological examination were 0.833 (95 % CI, 0.707-0.921) and 0.959 (95 % CI, 0.932-0.977), respectively. Discordant results were observed in 23 LNs (5.8 %), and these were mainly the result of tissue allocation bias and/or low CK19 protein expression. Conclusion: The OSNA assay can detect lymph node metastases in gastric cancer patients as accurately as the histological examination of blocks sectioned at 2-mm intervals. The OSNA assay is a useful tool for the intraoperative diagnosis of LN metastasis in gastric cancer patients.