Overexpression of wild-type c-RET and zero prevalence of RET/PTC rearrangements are associated with papillary thyroid cancer (PTC) in Kuwait

Absence of RET/PTC1 rearrangement in a sample of Colombian individuals with papillary thyroid carcinoma

Introduction: Papillary thyroid carcinoma is the most common endocrine neoplasm; therefore, markers with possible prognostic utility have been evaluated.Objective: To analyze the presence of RET/PTC1 rearrangement, lymphocytic thyroiditis and associated clinical features in patients with papillary thyroid cancer treated at the Hospital de San José in Bogotá, Colombia.Materials and methods: Clinical records of patients with complete thyroidectomy and diagnosis of papillary cancer were retrospectively identified. RNA was extracted from tumor tissue, and cDNA was obtained using inverse transcriptase to detect the rearrangement of the RET/PTC1 gene by means of qPCR.Results: 55 patients with papillary thyroid cancer were selected; 93% were females, and the mean age was 45.8 years. The most frequent histological variant was classic (49%). A relationship was found between lymphocytic thyroiditis and the number of positive nodes in segments other than central draining, as well as thyroiditis and antithyroid antibody value. No RET/PTC1 rearrangement expression was found.Conclusions: A relationship between lymphocytic thyroiditis and the number of positive nodes in segments other than central draining was found. Other molecular markers should be searched to differentiate the prognosis of these patients.

RAS Mutations, and RET/PTC and PAX8/PPAR-gamma Chromosomal Rearrangements Are Also Prevalent in Benign Thyroid Lesions: Implications Thereof and A Systematic Review

BACKGROUND

Molecular markers associated with thyroid malignancy are increasingly being used as differential diagnostic tools for thyroid nodules. However, little has been reported recently regarding the prevalence of these markers in benign lesions. The literature was systematically reviewed to examine studies that reported on the prevalence of these markers in benign thyroid lesions.

METHODS

Appropriate studies published between January 1, 2000, and April 30, 2015, and cataloged in PubMed, Embase, Cochrane, Scopus, and Web of Science databases were searched for by combining different keywords for "thyroid tumor" with both general and specific keywords for "molecular marker" by using "AND" as the Boolean operator. All studies meeting criteria that reported the prevalence of RAS mutations, and RET/PTC and PAX8/PPAR-gamma chromosomal rearrangements in benign thyroid lesions were included for study.

RESULTS

A total of 64 articles (including 8162 patients, of whom 42.5% had benign lesions) that met all the study criteria were systematically reviewed and abstracted. Among 35 studies examining RAS mutations, the reported prevalence of RAS mutation in benign lesions ranged from 0% to 48%. In 38 studies examining RET/PTC rearrangements, the prevalence in benign lesions ranged from 0% to 68%. PAX8/PPAR-gamma rearrangements were examined in 27 studies, with the prevalence in benign lesions ranging from 0% to 55%.

CONCLUSION

The presence of these biomarkers and the tremendous variation in reports of their prevalence in benign lesions suggests the need for caution when including these markers in diagnostic decisions. Further understanding of the importance of these markers, as well as newly discovered markers of thyroid malignancy, may be required in order to avoid overtreatment of patients with benign thyroid tumors.

RET/PTC rearrangement in benign and malignant thyroid diseases: a clinical standpoint

Cytological examination of fine needle aspiration biopsy is the primary means for distinguishing benign from malignant nodules. However, as inconclusive cytology is very frequent, the introduction of molecular markers in the preoperative diagnosis of thyroid nodules has been proposed in recent years. In this article, we review the clinical implications of preoperative detection of rearrangements of the RET gene (RET/papillary thyroid carcinoma (PTC)) in thyroid nodules. The prevalence of RET/PTC in PTC depends on the histological subtypes, geographical factors, radiation exposure, and detection method. Initially, RET/PTC was considered an exclusive PTC hallmark and later it was also found sporadically in benign thyroid lesions. More recently, the very sensitive detection methods, interphase fluorescence in situ hybridization (FISH) and Southern blot on RT-PCR amplicons, demonstrated that the oligoclonal occurrence of RET rearrangement in benign thyroid lesions is not a rare event and suggested that it could be associated with a faster enlargement in benign nodules. For this reason, RET/PTC cannot be considered as an absolute marker of PTC, and its diagnostic application must be limited to assays able to distinguish between clonal and oligoclonal expression. Detection of RET/PTC by quantitative assays will be useful for diagnostic purposes in cytology specimens when a precise cutoff will be fixed in a clinical setting. Until that time, less sensitive RET/PTC detection methods and FISH analysis remain the most appropriate means to refine inconclusive cytology. Future studies with a long follow-up will further clarify the clinical significance of low level of RET rearrangements in benign nodules.