Analysis of ret/PTC Gene Rearrangements Refines the Fine Needle Aspiration Diagnosis of Thyroid Cancer

Abstract

Papillary carcinoma (PC) represents the most common malignancy of the thyroid gland. Therefore, the assessment of fine needle aspiration biopsies of thyroid nodules rests heavily on the identification of nuclear features of PC. The ret/PTC oncogene, formed by several gene rearrangements, is specific for PC among thyroid tumors. In this study we examined thyroid aspirates for the presence of ret/PTC gene rearrangements by RT-PCR and Southern hybridization. We prospectively collected thyroid aspirates in Cytolyt solution and prepared slides for cytological examination using the ThinPrep method. All remaining material was then used for nucleic acid extraction with subsequent RT-PCR for the housekeeping gene PGK-1 to ensure ribonucleic acid integrity, for thyroglobulin to ensure the presence of follicular epithelial cells, and for the three most common ret/PTC gene rearrangements (ret/PTC-1, -2, and -3). The results of the first 73 cases with surgical follow-up were correlated with the cytological diagnosis and final histopathology. ret/PTC gene rearrangements were detected in 17 of 33 samples (52%) that were PC on histopathology; the presence of gene rearrangements was confirmed by molecular analysis of corresponding surgically resected frozen tissue. There were no false positives. The identification of ret/PTC gene rearrangements refined the diagnosis of PC in 9 of 15 specimens (60%) that would otherwise have been considered indeterminate and in 2 of 6 that were considered insufficient for cytological diagnosis. The results indicate that RT-PCR for ret/PTC is a specific marker that can be applied to fine needle aspiration biopsies and improves the diagnosis of malignancy when used as an adjunct to traditional cytology.

Utilization of ancillary studies in thyroid fine needle aspirates: A synopsis of the National Cancer Institute Thyroid Fine Needle Aspiration State of the Science Conference

“…22,23 RET/PTC chromosomal rearrangements also appear to be very promising for the diagnosis of papillary carcinoma, particularly in cases with challenging cytomorphological features. 24 The specificity of BRAF, RET/PTC, and other markers for thyroid carcinoma is very promising, but limited validation precludes their widespread clinical use.…”

Break–apart interphase fluorescence in situ hybridization assay in papillary thyroid carcinoma: on the road to optimizing the cut-off level for RET/PTC rearrangements

“…Finding an accurate, reliable, and clinically pragmatic strategy for RET/PTC detection becomes imperative because the detection of RET/PTC has been offered as a diagnostic tool for PTC in the surgical and preoperative cytological material (3,21,40,41,42,43,44). FISH is considered as the assay of choice for rearrangement detection on formalinfixed surgical samples (71) and according to Marotta et al…”

“…Thus, finding a reliable and biologically relevant strategy for RET/PTC detection may have important clinical and diagnostic implications as the detection of RET/PTC has been offered as a diagnostic tool for PTC in the surgical and preoperative cytological material (40,41,42,43,44,45). Moreover, the emergence of drugs that selectively inhibit RET kinase activity highlights the need of a better understanding of RET/PTC distribution within the tumor volume and of standardization of the detection methods for this rearrangement (46,47,48,49).…”

Application of molecular biology of differentiated thyroid cancer for clinical prognostication

“…To date, molecular characterisation of DTC has found its main clinical application in the diagnostic setting. Since the beginning of 2000s, several authors tried to use genetic findings for improving pre-surgical diagnosis of thyroid nodules showing indeterminate cytology (Cheung et al 2001, Xing et al 2004, Sapio et al 2007). During subsequent years, the continuous discovery of genetic abnormalities related to DTC and the development of the NGS techniques, which allowed the simultaneous analysis of a large number of molecular alterations, led to the development of mutational panels specifically dedicated to pre-surgical diagnosis of DTC on cytology samples.…”