Mutation of RET codon 768 is associated with the FMTC phenotype

Multiple endocrine neoplasia type 2A (MEN 2A), type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC) are inherited cancer syndromes resulting from mutations in the RET proto-oncogene. Missense mutations of five codons in exons 10 and 11 are found in both MEN 2A and FMTC families, while mutations at codon 768 in exon 13 have been identified in three FMTC families. We report here the results of mutation analysis on a large multi-generation family with multiple cases of medullary thyroid carcinoma (MTC) or C-cell hyperplasia and two individuals with isolated adrenal medullary hyperplasia. A mutation in exon 13, which alters codon 768 from a GAG (Glu) to a GAC (Asp), was found to segregate with the FMTC phenotype in this family but not with the adrenal medullary hyperplasia. These findings suggest that the codon 768 mutation does not predispose to adrenal medullary hyperplasia, but is an accurate predictor of the MTC phenotype in this family.     

The pathology of preclinical medullary thyroid carcinoma

Medullary carcinoma of the thyroid (MTC) occurs sporadically, or in familial forms in familial medullary thyroid carcinoma and multiple endocrine neoplasia types 2A and 2B. In the familial forms it is associated with well-characterized, germline mutations in the RET protooncogene. The mutation sites differ in MEN2A and MEN2B, and MTC develops at an earlier age and is more aggressive in MEN2B. Screening of relatives of affected individuals for such mutations can identify those at risk of developing MTC and total thyroidectomy can be carried out in the first decade of life before the development of clinical disease. Analysis of such removed thyroid glands shows abnormalities of the parafollcular C-cells in almost all cases. The abnormalities range from C-cell hyperplasia, either diffuse or nodular, to microcarcinoma and occasionally frank MTC. The abnormalities are bilateral and affects the upper two thirds of the thyroid lobes. Microcarcinomas may be visible with the naked eye, but often they are identified only on microscopy. Histopathological examination of the entire gland is essential.     

C-Cell hyperplasia and medullary thyroid microcarcinoma

Since the discovery of the thyroid C-cell, considerable progress has been made regarding its origin, function, and pathology. In this article an attempt is made to summarize and update our knowledge about physiologic or reactive C-cell hyperplasia, neoplastic C-cell hyperplasia (medullary carcinoma in situ), and medullary microcarcinoma. Seldom recognized preoperatively, physiologic C-cell hyperplasia is associated with inflammatory, metabolic, and neoplastic thyroid disorders as well as with hypercalcemia. However, the pathogenesis is still unclear. Although physiologic C-cell hyperplasia may progress to medullary carcinoma, the full malignant potential is unknown. Problems related to the definition of physiologic C-cell hyperplasia are discussed. Immunohistochemistry and quantitative analysis are required for the diagnosis. By contrast, C-cell hyperplasia associated with MEN II syndromes or familial medullary carcinoma can be diagnosed preoperatively in asymptomatic children or adolescents by the detection of germline mutations of the RET protooncogene. Morphologic and genetic abnormalities support the idea that C-cells in the familial form of C-cell hyperplasia are neoplastic and can be recognized with conventional stains. Therefore, the number of C-cells is irrelevant for the diagnosis. Medullary microcarcinoma is a neoplasm that measures < 1 cm. The sporadic variant is usually an incidental microscopic finding, whereas the familial form can be diagnosed by genetic testing. Its morphologic features and biologic behavior differ from those of larger medullary carcinomas. The frequency of medullary microcarcinoma will probably increase with the use of genetic testing.     

Adrenal medullary hyperplasia. Hyperplasia-pheochromocytoma sequence

We present a case of unilateral adrenal medullary hyperplasia in a 63-year-old woman with clinical signs and symptoms of pheochromocytoma unassociated with multiple endocrine neoplasia. The surgically removed adrenal gland revealed diffuse medullary hyperplasia with multiple micronodules measuring up to 2 mm. The micronodules were composed of enlarged chromaffin cells with atypia, histologically similar to those of pheochromocytoma, forming small solid alveolar patterns separated by a fibrovascular stroma. Removal of the hyperplastic adrenal gland resulted in disappearance of paroxysmal nocturnal hypertension and palpitation. These results suggest that diffuse and nodular medullary hyperplasia is the precursor of pheochromocytoma.     

Ultrastructural study of thyroid medullary carcinoma.

This study deals with 11 cases of thyroid medullary carcinoma of which 7 were familial cases including 3 cases of Sipple's syndrome and 4 cases of sporadic cases. There were also 2 cases of Cushing's syndrome. In addition to the previously described English literatures about human medullary carcinoma of the thyroid, the rod-shaped body with cristae and an abundant glycogen particles in the cytoplasm, nuclear inclusion bodies of cytoplasmic invagination and microvilli at the surface membrane of gland formation were found in our cases. The mean and mode diameters of secretory granules of all familial cases with only calcitonin secretion were larger than those of the sporadic cases with ectopic ACTH and beta-MSH in addition to calcitonin secretion. Ultrastructural study on non-cancerous follicles of grossly normal thyroid of two cases of early familial medullary carcinoma disclosed apparently increased C-cells which were not intrathyroidal metastases. It is supposed that the increased C-cells in the thyroid of the familial cases are multicentric C-cell hyperplasia.     

Adrenal medullary hyperplasia: A clinicopathologic study of four cases

This study presents the clinicopathologic findings in four new cases of adrenal medullary hyperplasia. The patients presented with episodic hypertension frequently associated with palpitations headache, and diaphoresis. All four had elevated urinary catecholamine levels during attacks, and were thought clinically to have a pheochromocytoma. In each case laparotomy revealed a diffusely enlarged adrenal gland without a discrete tumor. Histologic examination of the adrenals demonstrated a diffuse or diffuse and nodular expansion of the medulla confirmed by morphometric study. Of the four patients, three underwent unilateral and one bilateral adrenalectomy. Two patients who underwent unilateral adrenalectomy have been free of symptoms for three years. Thus, it would appear that adrenal medullary hyperplasia may occur unilaterally or asynchronously in the two glands. The bilaterally adrenalectomized patient has had persistent attacks, suggesting that the stimulus to adrenal medullary hyperplasia may possibly affect other chromaffin tissues. On the basis of our cases and a review of the literature, we propose the following criteria for the diagnosis of adrenal medullary hyperplasia: a clinical history of episodic attacks suggesting pheochromocytoma (generally with associated increased urinary catecholamine levels), an adrenal gland showing diffuse expansion of the medulla into the alae or tail of the gland with or without nodule formation, a medulla composed of enlarged cells with or without pleomorphism, and, most important, an increased medulla/cortex ratio, together with an increased calculated medullary weight asddetermined by morphometric analysis.     

Familial Follicular Cell Tumors: Classification and Morphological Characteristics

Familial follicular cell-derived well-differentiated thyroid cancer, papillary (PTC), and follicular thyroid carcinomas (FTC), accounts for 95% of thyroid malignancies. The majority of are sporadic, and at least 5% of these patients will have familial disease. Familial thyroid syndromes are classified into familial medullary thyroid carcinoma (FMTC), derived from calcitonin-producing C cells, and familial follicular cell tumors or non-medullary thyroid carcinoma (FNMTC), derived from follicular cells. Twenty-five percent of patients with medullary thyroid cancer (MTC) have a familial form; however, this accounts for only 1% of all patients with thyroid cancer. The familial follicular cell-derived lesions or familial non-medullary thyroid cancer can be divided into two clinical-pathological groups. The first group includes familial syndromes characterized by a predominance of non-thyroidal tumors, such as familial adenomatous polyposis (FAP), PTEN-hamartoma tumor syndrome (Cowden disease; PHTS), Carney complex, Werner syndrome, and Pendred syndrome. The second group includes familial syndromes characterized by predominance of papillary thyroid carcinoma (PTC), such as pure fPTC, fPTC associated with papillary renal cell carcinoma, and fPTC with multinodular goiter. Most of the progress in the genetics of familial thyroid cancer has been in patients with MTC. This is usually a component of multiple endocrine neoplasias IIA or IIB, or as pure familial medullary thyroid carcinoma syndrome. The genetic events in the familial C-cell-derived tumors are known and genotype-phenotype correlations are well established. The mutations in patients with isolated NMFTC have not been as well defined as in MTC. In many cases, patients have a known familial syndrome that has defined risk for thyroid cancer. The clinician must be knowledgeable in recognizing the possibility of an underlying familial syndrome when a patient presents with thyroid cancer. Some characteristic thyroid morphologic findings should alert the pathologist of a possible familial cancer syndrome, which may lead to further molecular genetics evaluation.     

C-cell hyperplasia and medullary thyroid carcinoma: clinicopathological and genetic correlations in 66 consecutive patients.

Routine calcitonin (CT) assay programs and genetic testing for RET proto-oncogene mutations have consistently modified the management and understanding of C-cell proliferative disorders. We report a series of 66 consecutive patients with C-cell hyperplasia (CCH) or medullary thyroid carcinoma (MTC) observed in our institution within an 8-year time period. All the patients had a preoperative basal CT assay and an RET proto-oncogene sequencing. Seventeen patients (F-M ratio: 8:9, mean age: 29.7 y) had a multiple endocrine neoplasia Type 2: 3 children <10 years of age had CCH only, and 14 patients had an MTC, with neoplastic CCH in 10/14 cases. Twenty-seven patients (F-M ratio: 18:9, mean age: 56.6 y) had a sporadic MTC, with physiological CCH in 8 and neoplastic CCH in 3 cases. Twenty-two men (mean age: 46.2 y) had CCH only (physiological CCH in 17 men and neoplastic CCH in 5). We conclude that (1) clinical and pathological characteristics (familial MTC, tumor multifocality, neoplastic CCH) usually associated with hereditary MTC may be misleading and that on the contrary, RET sequencing gives no false positive result; (2) sporadic neoplastic CCH accompanies (and probably precedes) a number of sporadic MTC; and (3) women presenting with a sporadic elevated basal CT have a 100% risk of having an MTC (15/15), but this risk is 3-fold less in men (31%), who will most often have CCH only (69%).     

Penetrance of inherited medullary thyroid carcinoma and genotype-phenotype correlation in a large multiple endocrine neoplasia type 2A family with C634Y RET mutation

Multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC) are characterized by development of medullary thyroid carcinoma (MTC) and caused by germline RET mutations. Patients with MEN 2A also develop pheochromocytoma and/or hyperparathyroidism (HPT). However, MEN 2A-affected individuals could display the FMTC phenotype at first clinical manifestation. To establish the correct phenotype and improve clinical management of patients affected by hereditary MTC, clinical screening, RET mutational analysis, penetrance of MTC, and genotype-phenotype correlation were performed in a large, suspected FMTC kindred of 86 individuals. Germline C634Y RET mutation was confirmed in 22 individuals, 15 of whom were thyroidectomized when high serum calcitonin levels were detected. MTC was confirmed in 12 individuals and C-cell hyperplasia in 3. HPT was detected in two patients. High penetrance of MTC at young age (79% at 30 yr of age) was found. This family was considered to be affected by FMTC for several years because MTC was the sole clinical manifestation. However, our results allowed reclassifying the family as MEN 2A, thereby improving clinical management of family members. Our findings regarding penetrance and genotype-phenotype correlation suggest that patients considered to have FMTC may in fact have MEN 2A in some kindreds.     

von Recklinghausen's disease associated with somatostatin-rich duodenal carcinoid (somatostatinoma), medullary thyroid carcinoma and diffuse adrenal medullary hyperplasia.

This report describes the concomitant occurrence of a somatostatin-rich duodenal carcinoid, a medullary thyroid carcinoma and a diffuse adrenal medullary hyperplasia in a patient with von Recklinghausen's disease. A 50-year-old Japanese man died from lung metastasis of a malignant schwannoma. In addition to extensive viscero-cutaneous neurofibromatosis, two different types of neuroendocrine tumors were found in the duodenum and thyroid gland at autopsy. The duodenal tumor, which was located in the second portion, showed the histologic appearance of a carcinoid tumor with glandular differentiation and psammoma-bodies. Immunohistochemically the tumor cells were intensely positive for somatostatin. The thyroid tumor was composed of nests of tumor cells arranged in an endocrine pattern, and showed immunoreactivity for calcitonin. A review of the literature revealed no previously reported case of concomitant occurrence of duodenal somatostatinoma and medullary thyroid carcinoma in a single patient with von Recklinghausen's disease. Morphometric analysis of adrenal glands disclosed the presence of diffuse medullary hyperplasia. Thus, the present case exhibited a similarity in some respects with multiple endocrine neoplasia (MEN) syndrome, Type IIa or IIb.     

Tenascin C in medullary thyroid microcarcinoma and C-cell hyperplasia

Tenascin C (Tn-C) is an extracellular matrix glycoprotein that is expressed early in carcinogenesis including intraepithelial neoplastic lesions of different organs. In this study, we analyze whether stroma reaction seen by Tn-C expression is detected early in tumorigenesis of medullary thyroid carcinoma (MTC) including medullary microcarcinoma and C-cell hyperplasia (CCH), which is accepted to be a precursor lesion of MTC in the setting of RET oncogene germ-line mutation. Tn-C was expressed in the stroma of all medullary microcarcinoma and in the stroma next to CCH. Stromal Tn-C expression was significantly more often seen in CCH with concomitant MTC than in isolated CCH of hereditary as well as nonhereditary cases (p = 0.001 and p = 0.016, respectively). We conclude that Tn-C expression and thus early stroma remodeling is seen in medullary microcarcinoma and CCH. Stromal Tn-C expression seems to be an indicator of a further step in carcinogenesis of MTC irrespective of a RET oncogene germ-line mutation.     

Penetrance of inherited medullary thyroid carcinoma and genotype-phenotype correlation in a large multiple endocrine neoplasia type 2A family with C634Y RET mutatiom

Multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC) are characterized by development of medullary thyroid carcinoma (MTC) and caused by germline RET mutations. Patients with MEN 2A also develop pheochromocytoma and/or hyperparathyroidism (HPT). However, MEN 2A-affected individuals could display the FMTC phenotype at first clinical manifestation. To establish the correct phenotype and improve clinical management of patients affected by hereditary MTC, clinical screening, RET mutational analysis, penetrance of MTC, and genotype-phenotype correlation were performed in a large, suspected FMTC kindred of 86 individuals. Germline C634Y RET mutation was confirmed in 22 individuals, 15 of whom were thyroidectomized when high serum calcitonin levels were detected. MTC was confirmed in 12 individuals and C-cell hyperplasia in 3. HPT was detected in two patients. High penetrance of MTC at young age (79% at 30 yr of age) was found. This family was considered to be affected by FMTC for several years because MTC was the sole clinical manifestation. However, our results allowed reclassifying the family as MEN 2A, thereby improving clinical management of family members. Our findings regarding penetrance and genotype-phenotype correlation suggest that patients considered to have FMTC may in fact have MEN 2A in some kindreds.     

Familiäre Karzinome der Schilddrüse

Approximately 5% of differentiated thyroid carcinomas with follicular cell differentiation, papillary thyroid carcinoma (PTC) and follicular thyroid carcinoma (FTC) and 25–30% of medullary thyroid carcinoma (MTC) are hereditary. They occur either as part of a defined syndrome or are confined to the thyroid gland. Compared to their sporadic non-hereditary counterparts hereditary thyroid carcinomas generally develop earlier and regularly show multifocal tumour growth. With the exception of familial MTC, which is preceded by neoplastic C cell hyperplasia, no precursor lesions of hereditary thyroid carcinoma are known. In strong correlation with the localisation of the germline mutation of the RET protooncogene, familial MTC shows a distinct clinical course which allows precise clinical decision-making for prophylactic thyroidectomy to prevent invasive MTC. According to current knowledge prophylactic thyroidectomy of all other types of hereditary thyroid carcinoma is not justified.     

家族性甲状腺髓样癌的基因相关性研究

甲状腺髓样癌(medullary thyroid carcinoma,MTC)的发病率约占甲状腺癌发病率的5%～10%,而家族性甲状腺髓样癌(familial medullary thyriod carcinoma,FMTC)的发病率约占甲状腺髓样癌发病率的20%左右,且发病率有不断增高的趋势.目前公认RET原癌基因(编码受体酪氨酸激酶)是导致FMTC的主要原因.PET基因仅通过点突变即可以导致甲状腺癌的发生.该文对RET原癌基因的正常功能以及与FMTC的相关性研究作一综述.

Abstract：

About 5%～10% of thyroid carcinoma is medullary thyroid carcinoma(MTC),of which,about 20% are familial medullary thyriod carcinoma(FTMC).There is a trend that the incidence has been noticed to increase.Currently it has been known that RET proto-oncogene(encoding receptor tyrosine kinase)is only gene involved in the pathogenesis of FTMC.In this particle,We will view the function of PET proto-oncogene and its association with FTMC.     

Cytogenetics of multiple endocrine neoplasia syndromes. I. Two different, unique clonal chromosome changes in a medullary thyroid carcinoma and in a C-cell thyroid hyperplasia.

In short-term cultures of tumor tissue from a medullary thyroid carcinoma (MTC), we found a large clone of cells with a balanced translocation t(9;12)(p24;q22). A large clone with a balanced translocation t(10;16)(p11;q24) was also found in cultures from a C-cell thyroid hyperplasia. No clearcut evidence for chromosome instability was observed in the lymphocytes of the two patients. The mother of the first patient died of MTC; two relatives of the second patient had MTC and one of them had pheochromocytoma. These findings classify the two subjects as MEN 2A patients with different phenotypic expression but with the same type of chromosomal abnormality.     

Primary hereditary medullary thyroid carcinoma – C-cell morphology and correlation with preoperative calcitonin levels

 Early thyroidectomy offers an opportunity of preventing the development of medullary thyroid carcinoma (MTC) in patients at risk for hereditary MTC. We investigated the thyroid glands of 32 patients with hereditary MTC to identify the changes in C-cell morphology and to correlate these with plasma calcitonin (CT) levels and with clinical data. The entire thyroid gland was processed for histological examination including immunostaining for CT. All glands revealed C-cell hyperplasia (CCH), and MTC was found in 21 patients (66% of 32, youngest patient 6 years, youngest with lymph node metastases [LNM] 17 years). The transition from CCH to MTC was characterized by destruction of the follicular basement membrane and by diminished intensity of CT immunostaining. Normal plasma CT levels after provocation with pentagastrin were found only in patients with CCH. Basally elevated plasma CT levels were restricted to MTC. LNM were only found in multifocal tumours at least 4 mm in diameter. It is not yet clear whether or not CCH in patients at risk for hereditary MTC is a neoplastic change, but in these patients the term ’C-cell hyperplasia’ is of doubtful value. All MEN gene carriers reveal CCH, and almost all of them will develop multifocal MTC, so that CCH is probably a precursor lesion of an indubitably malignant tumour. Prophylactic thyroidectomy is justified at the age of 6 to anticipate development of a MTC. Lymphadenectomy is necessary in children if they are older than 10 years or have elevated plasma CT levels. Received: 30 January 1998 / Accepted: 25 March 1998     

Sustentacular cells occur frequently in the familial form of medullary thyroid carcinoma

The presence and distribution of S-100-immunoreactive sustentacular cells were investigated by immunohistochemistry in 67 medullary thyroid carcinomas (MTCs). The familial or sporadic status of the tumours was assessed by clinical data and confirmed by the identification of RET germline mutations using the polymerase chain reaction–single-strand conformation polymorphism (PCR–SSCP) and restriction analysis. Sustentacular cells were detected in 19 tumours (28·3 per cent). They were found significantly more frequently in the familial (15/24, 62·5 per cent) than in the sporadic MTCs (4/43, 9·3 per cent). The results indicate that sustentacular cells are commonly found in familial MTC and their presence in any MTC may be regarded as an indirect indicator that the tumour might be of the familial type. © 1998 John Wiley & Sons, Ltd.     

Mutational analysis of the RET proto-oncogene in 71 Japanese patients with medullary thyroid carcinoma

Multiple endocrine neoplasia types 2A and 2B (MEN2A and MEN2B) and familial medullary thyroid carcinomas (FMTC) are caused by germline mutations in the RET proto-oncogene. To investigate the spectrum of RET mutations among Japanese patients, we screened the RET gene in 71 patients with thyroid carcinomas. The panel included representatives of 44 families carrying FMTC or MEN2, 22 sporadic medullary thyroid carcinomas (MTCs), and five MTCs without familial information. Mutations in nucleotide sequences encoding one of three specific cysteine residues in the extracellular domain of the RET protein were found in 33 of the 34 MEN2A patients and in five of the six FMTC patients examined. A mutation at codon 918, causing the substitution of threonine for methionine in the tyrosine kinase domain of the protein, was found in germline DNAs of all four patients with MEN2B and in two of the 22 patients with sporadic MTCs; codon 918 was mutated somatically in tumor DNAs from three other sporadic cases. Germline mutations of codon 768, GAG to GAC (Glu to Asp), were detected in one FMTC, in one patient with sporadic MTC, and in one of the patients without familial information. Two somatic mutations, an Asp to Gly substitution at codon 631 and a Cys to Arg substitution at codon 634, had not been reported previously. Of five germline mutations found among the 22 sporadic cases, four were confirmed as de novo mutations since in each case neither parent carried the mutation. As nearly one-fourth of the patients with sporadic MTCs carried germline mutations and 50% of their children are expected to develop MTC and other endocrine tumors, these results indicated the importance of careful clinical surveillance of family members of any patient with MTC. Received: August 22, 1997 / Accepted: October 22, 1997