Introduction/Background One-step nucleic acid amplification (OSNA) is an automated molecular diagnostic assay used to detect metastases by analyzing the levels of cytokeratin 19 mRNA in whole lymph nodes. It has been validated as an accurate and reliable tool for staging in several types of cancers and is included in the National Institute for Health and Care Excellence guidelines for the management of breast cancer. The objective of this study was to evaluate the efficacy of OSNA for the detection of sentinel lymph node (SLN) metastasis compared to standard pathological ultrastaging in patients with early-stage endometrial cancer (EC).

Methodology A total of 526 SLNs from 191 patients with EC were included in the study, and 379 SLNs (147 patients) were evaluated by both methods, OSNA and standard pathological ultrastaging. The central 1 mm portion of each lymph node was subjected to semi-serial sectioning at 200  m intervals and examined by hematoxylin–eosin and immunohistochemistry with CK19; the remaining tissue was analyzed by OSNA for CK19 mRNA.

Results The OSNA assay detected metastases in 19.7% of patients (14.9% micrometastasis and 4.8% macrometastasis), whereas pathological ultrastaging detected metastasis in 8.8% of patients (3.4% micrometastasis and 5.4% macrometastasis). Using the established cut-off value for detecting SLN metastasis by OSNA in EC (250 copies/L), the sensitivity of the OSNA assay was 92%, specificity was 82%, diagnostic accuracy was 83%, and the negative predictive value was 99%. Discordant results between both methods were recorded in 20 patients (13.6%). OSNA resulted in an upstaging in 12 patients (8.2%).

Conclusion OSNA provides fast and reliable results and has already been successfully incorporated in the standard treatment guidelines for other tumors. In EC, the OSNA method shows higher sensitivity, specificity, and diagnostic accuracy in the detection of SLN metastasis, including low-volume metastasis, compared to pathological ultrastaging.

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Abstract #697 Figure 1

Disclosures The authors declare no conflict of interest regarding this study.

ENDO-OSNA was funded by a grant from Sysmex España S.L.

The funder had no role in the design of the study; in the analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results; but provided support for data collection.

ROC curve showing the OSNA assay vs. pathological ultrastaging for the detection of SLN metastasis in endometrial cancer.