Analysis ofRET protooncogene point mutations distinguishes heritable from nonheritable medullary thyroid carcinomas

Abstract

Background. The distinction of sporadic from inherited medullary thyroid carcinomas (MTCs) is of clinical importance because of the differences in prognosis, and the need for family screening for genetic counseling required in the latter. Germline mutations in the RET protooncogene are associated with multiple endocrine neoplasia (MEN) type 2A, familial medullary thyroid carcinoma (FMTC), and MEN type 2B. Somatic point mutations in the same gene have been identified in a subset of sporadically occurring medullary thyroid carcinomas. Methods. A nonisotopic polymerase chain reaction‐(PCR) based single strand conformation polymorphism (SSCP) analysis and heteroduplex gel electrophoresis method was used to screen DNA extracted from 32 form‐aldehyde fixed and paraffin embedded MTC specimens and normal tissue or blood of the same patient for point mutations in RET exons 10, 11, and 16. Point mutations were identified by nonisotopic cycle sequencing of PCR‐products using an automated DNA‐sequencer. Results were compared with the disease phenotype, clinical findings, and follow‐up. Results. Six different missense germline mutations were identified at cysteine residues 618, 630, and 634 of the cysteine‐rich extracellular RET domain encoded by exons 10 and 11 in all patients with FMTC and MEN 2A. The frequency of mutations at codon 634 was higher in patients with MEN 2A than with FMTC and a 634 Cys → Arg mutation was associated with parathyroid disease in three patients. A germline Met → Thr point mutation at codon 918 of the RET tyrosine kinase domain was identified in all three patients with MEN 2B. Two patients with clinically sporadic MTCs and negative family history exhibited a RET germline mutation at codon 634, indicating the presence of an nonpredicted inherited MTC. Further‐more, one patient had a 618 Cys → Ser mutation in the tumor and nontumorous thyroid DNA but not in blood DNA, indicating a mosaic mutation affecting thyroid tissue but not blood cells. Tumor specific (somatic) Met → Thr point mutations at codon 918 were identified in 5 of 13 sporadic MTCs. The remaining eight sporadic MTCs lacked mutations in all three RET exons tested. Conclusions. This study demonstrates that (1) the molecular methods are not only suitable to identify asymptomatic individuals at risk for MEN 2A, FMTC, and MEN 2B but also to distinguish heritable from non‐heritable MTCs using archival tissue specimens, and (2) that more MTCs than clinically expected are heritable, indicating the need for genetic analysis of all patients with MTC. Cancer 1995; 76:479–89.

What is New on Thyroid Cancer Biomarkers

“…These differences have a practical application because the recognition of each RET germ-line mutation leads to an unequivocal diagnosis of hereditary MTC. Furthermore, RET germinal mutations are employed to identify inherited MTC, both isolated and occurring in MEN (Komminoth et al 1995; Fink et al 1996). Specifically, the germinal mutations involving the exons 10 and 11 are associated with MTC appearing in MEN 2A, while the germinal mutation of the exons 16 is linked to MTC arising in MEN 2B.…”

Trends in the presentation, treatment, and survival of patients with medullary thyroid cancer over the past 30 years

“…Genetic testing for RET proto-oncogene mutations is now available and recommended for anyone with a diagnosis of MTC (8). If a germline mutation is identified, relatives can be screened, and carriers can be treated prophylactically with a total thyroidectomy (9). In addition, tumor markers, such as calcitonin and carcinoembryonic antigen (CEA), help guide the initial extent of surgery and facilitate earlier detection of recurrence (8).…”

Case Report of a Medullary Thyroid Carcinoma and Hyperparathyroidism in Patient with Ret Proto Oncogene Positive

“…Of the 18 immediate family (6 kids, 9 siblings and 3 nephews, sons of a deceased brother) in whom the genetic study of the RET oncogene was performed at the Hospital de Clinicas in Sao Paulo, two sons of the patient, the first male (33) and one female (18) were positive and led to surgery (total thyroidectomy). (Figure 6), (Figure 7)…”

“…16 The RET oncogene test has been pre-operatively recommended in all patients with Medullary carcinoma. [17][18][19] Eng and colleagues 20 estimated that a patient without a known RET mutation Germ line has a 0.5% chance of MEN 2A and 3% of FMTC. The 10-year survival of patients with tumors confined to the thyroid gland tumors is 95.6%, those with metastases to regional lymph nodes is 75.5% and those with distant metastases is only 40%.…”