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 t umors. 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 speci fic messenger RNAs (mRNA), such as those transcribed from the RET proto-onc ogene, 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 met hod for the molecular diagnosis of thyroid tumors without additional invasi on to the patient by extracting RNA for RT-PCR from the leftover cells insi de the needles used for fine needle aspiration biopsy (Aspiration Biopsy-Re verse Transcription-Polymerase Chain Reaction, ABRP). By applying the ABRP method to the detection of RET, calcitonin, and CEA mRNAs, an accurate mole cular-based diagnosis for MTC may be established as an adjunct to cytologic al diagnosis. In this study, 35 aspirates were obtained at the time of surg ery from thyroid tumors, including 11 MTCs. The expression of these mRNAs i n the leftover cells inside the needles used for the aspiration was then ex amined. 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 n ormal thyroid tissues. Furthermore, MTC was preoperatively diagnosed in thr ee patients by ABRP detection of these mRNAs, and these diagnoses were conf irmed by subsequent cytological and histopathological analyses. Thus RT-PCR detection of RET, calcitonin, and CEA mRNAs in FNABs may be an efficient m olecular adjunct for diagnosing MTC.