Expression Analysis of Selected mRNA Is Potentially Useful in the Fine Needle Aspiration Diagnosis of Papillary Thyroid Carcinoma
T Scognamiglio, N Kitabayashi, TJ Fahey III, Y-T Chen. Weill Cornell Medical College, New York, NY
Background: Gene expression analysis has identified a series of genes that show consistent differential expression between papillary thyroid carcinoma (PTC) and benign nodules. Genes consistently upregulated in PTC include high mobility group protein gene (HMGA2), keratin 19 (KRT19) and galectin-3 (LGALS3), whereas peroxidase (TPO), deiodinase 1 (DIO1), and trefoil factor 3 (TFF3) are downregulated. In this study, we sought to evaluate whether mRNA analysis of this panel of markers can reliably distinguish benign thyroid lesions from PTC, particularly in the setting of fine needle aspiration (FNA).
Design: Real time quantitative PCR was used to evaluate the mRNA expression of HMGA2, KRT19, LGALS3, TPO, DIO1, and TFF3 in 41 fresh frozen tissue (FFT) and 39 ex vivo FNA samples. FFT samples included 4 normal thyroid, 16 follicular adenoma (FA) and 21 PTC, including 2 follicular variant of papillary thyroid carcinoma (FVPTC) and 19 classical PTC (CPTC). FNA samples included 9 hyperplastic lesions (HP), 10 FA, 10 CPTC, and 10 FVPTC. The Ct (PCR cycle number at threshold) value for each gene was obtained and the combined Ct value differences between the 3 upregulated genes (HGMA2+KRT19+LGALS3) and 3 downregulated genes (TPO+DIO1+TFF3) were calculated for each sample, designated as delta Ct. The delta Ct values from the benign and malignant groups were plotted and compared, and a cut-off value was established as a molecular criterion for diagnosing PTC.
Results: In the FFT samples, the molecular criterion accurately classified all PTCs as malignant and 15/16 of the FA as benign, with 1 FA mis-classified as PTC, corresponding to a specificity of 93.7% and a sensitivity of 100%. For the FNA samples, all FA were classified as benign while 15/20 PTC were correctly identified, corresponding to 100%specificity and 80% sensitivity for the diagnosis of PTC. The lower sensitivity in the FNA specimens (vs. in the FFT group) is likely due to contamination of non-neoplastic cells and/or suboptimal RNA yields and quality.
Conclusions: Gene expression of the selected gene panel is useful in distinguishing benign thyroid lesions from PTC. In the setting of FNA, this molecular assay is highly specific for diagnosing PTC but not as sensitive. This limitation in sensitivity is predictable for all morphology-free molecular assays as normal tissue contamination is inevitable in most FNAs. We conclude that this assay can be valuable in helping establish the diagnosis of PTC in cytologically inconclusive FNA specimens.
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 42, Wednesday Afternoon