Preoperative diagnosis of medullary thyroid carcinoma by RT-PCR using RNA extracted from leftover cells within a needle used for fine needle aspiration biopsy

Fine needle aspiration Biopsy (FNAB) is commonly used to diagnose thyroid tumors. In some clinical situations, however, accurate diagnosis requires a more objective method than cytological examination alone. Medullary thyroid carcinomas (MTC) derive from C cells in the thyroid and express some specific messenger RNAs (mRNA), such as those transcribed from the RET proto-oncogene, the calcitonin gene, and the gene for carcinoembryonic antigen (CEA), which usually do not exist in normal thyroid follicular cells or thyroid tumors of follicular epithelial descent. Recently, we established a new method for the molecular diagnosis of thyroid tumors without additional invasion to the patient by extracting RNA for RT-PCR from the leftover cells inside the needles used for fine needle aspiration biopsy (Aspiration Biopsy-Reverse Transcription-Polymerase Chain Reaction, ABRP). By applying the ABRP method to the detection of RET, calcitonin, and CEA mRNAs, an accurate molecular-based diagnosis for MTC may be established as an adjunct to cytological diagnosis. In this study, 35 aspirates were obtained at the time of surgery from thyroid tumors, including 11 MTCs. The expression of these mRNAs in the leftover cells inside the needles used for the aspiration was then examined. Transcripts from all three genes were detected in the samples from all 11 MTCs, but none of these mRNAs were detected in the other tumors or normal thyroid tissues. Furthermore, MTC was preoperatively diagnosed in three patients by ABRP detection of these mRNAs, and these diagnoses were confirmed by subsequent cytological and histopathological analyses. Thus RT-PCR detection of RET, calcitonin, and CEA mRNAs in FNABs may be an efficient molecular adjunct for diagnosing MTC.