This study demonstrated the analytical and clinical validity of a pairwise microRNA (miRNA) analysis for the detection of medullary thyroid cancer (MTC) using ThyraMIR® Thyroid miRNA Classifier.
miRNA classification was based on a clinically validated panel of 10 specific miRNAs performed by quantitative real-time polymerase chain reaction. Diff-pair analysis was performed by subtracting the critical threshold value of one miRNA from the critical threshold values of other miRNAs. Next-generation sequencing with the ThyGeNEXT® mutation panel identified oncogenic gene alterations.
The discovery cohort consisted of 30 formalin-fixed, paraffin-embedded benign and malignant thyroid neoplasms, including 4 cases of MTC. After analytical validation, clinical validation was performed using 3 distinct cohorts (a total of 7,557 specimens). Clinical FNA samples included dedicated needle passes placed directly into preservative solution or cytology slides.
The assay correctly classified all MTC and non-MTC samples in the analytical validation study and in the 3 clinical validation cohorts. Pairwise analysis further demonstrated that, when compared with the other 9 miRNAs of the ThyraMIR® panel, miR-375 was highly expressed in MTC but not in other thyroid histopathologic categories.
The overall test accuracy was 100% (95% confidence interval, 99%-100%) and the specificity was 100% (95% CI, 99%-100%) in indeterminate FNA cytology samples. The sensitivity of the diff-pair analysis was greater than that of the MTC-specific mutation panel analysis (100% vs 25%; P=.03)
The use of this unique combination testing approach provided value to samples with a Bethesda III (atypia of undetermined significance/follicular lesion of undetermined significance) or IV (follicular neoplasm/suspicious for neoplasm) cytology diagnosis, particularly in the absence of cytological features of MTC.
Pairwise miRNA expression analysis of ThyraMIR® results accurately identified MTC in thyroid FNA samples, including those with indeterminate FNA cytology findings.