621 Background: miR-371a-3p (miR371) is a promising biomarker in GCTs. Diagnostic parameters of miR371 in the literature utilize different laboratory techniques, testing protocol, standards, and thresholds, potentially limiting cross-study comparison and generalized adoption. Establishing assay concordance and standardization is important before implementing the assay in clinical practice. Methods: The primary objective was to assess agreement between paired miR371 test results from the Memorial Sloan Kettering Cancer Center (MSK) and University of California San Diego (UCSD) assays, which differ in technique, testing protocol, analytical thresholds, and cutoff criteria, among chemotherapy naïve patients prior to orchiectomy or RPLND surgery. All samples were analyzed in CLIA-certified labs at both centers. An a piori sample size of 56 paired samples was determined to achieve 91% power to differentiate between 75% unacceptable agreement (null) versus 90% acceptable agreement (alternative) using a one-sided exact test with alpha 0.05. A minimum concordance of 48 of 56 paired test results was required to reject the null hypothesis of unacceptable agreement. Secondary objectives were to compare and quantify variation between paired Ct values and to assess assay performance characteristics in detecting active disease (defined as presence of non-teratomatous GCT ntGCT at surgery). Samples were randomly selected from those available at each institution, stratified to achieve approximately equal numbers of samples by site (MSK/UCSD), disease status (active/not active), and clinical setting (pre-orchiectomy/pre-RPLND). Results: Samples were categorized by clinical setting (pre-orchiectomy: n=27, pre-RPLND: n=29) and disease status (active: n=31, not active: n=25) and compared by institution. Assay agreement was 87.5% (95% CI: 75.9%, 94.8%), and the Spearman correlation coefficient between the two assays was 0.84 (95% CI: 0.74, 0.90). Forty nine of 56 samples demonstrated concordance allowing rejection of the null hypothesis. Both assays exhibited strong performance characteristics (Table). Conclusions: The primary objective of this cross-laboratory comparison was achieved, demonstrating concordance between the MSK and UCSD miR371 assays. Further cross-institutional comparisons in defined clinical settings will facilitate collaboration and widespread clinical adoption of the miR371 test. Additional clinical data will be presented. MSK ntGCT+ ntGCT- Total UCSD ntGCT+ ntGCT- Total miR371+ 29 3 32 miR371+ 30 3 33 miR371- 2 22 24 miR371- 1 22 23 Total 31 25 56 Total 31 25 56 Sensitivity 94 Sensitivity 97 Specificity 88 Specificity 88 PPV 91 PPV 91 NPV 92 NPV 96 AUC 92 AUC
Levin et al. (2026) studied this question.