Expression of the RET proto-oncogene in papillary thyroid carcinoma and its correlation with clinical outcome

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Abstract
Background: In papillary thyroid carcinoma (PTC), presence of the oncogenes RET/PTC has been described, but their correlation with prognosis is debated. The aim of this study was to investigate the expression of the RET proto-oncogene (RET) and correlate it with clinical outcome. Methods: Sixty-one PTCs were analysed for expression of RET and the oncogenes RET/PTC1–4 by polymerase chain reaction of complementary DNA. Results: Twenty-nine PTCs (48 per cent) expressed the RET tyrosine kinase domain (RET-TK). Twelve expressed wild-type RET (WT-RET). One tumour expressed RET/PTC3, one a variant of RET/PTC3, and one RET/PTC1 and WT-RET simultaneously. The remaining 14 expressed RET-TK only. WT-RET expression was detected more frequently in poorly differentiated PTCs (P < 0·05) and in PTCs from patients with aggressive disease (P < 0·01). WT-RET expression remained an independently significant risk factor for aggressive disease when analysed together with other recognized risk factors using a stepwise multiple logistic regression model. Conclusion: Almost half of the PTCs showed RET-TK expression; in only three was this explained by expression of a RET/PTC rearrangement. Instead, expression of WT-RET was detected in 45 per cent of the RET-TK-positive tumours and this expression was an independently significant risk factor for aggressive PTC.