Novel point mutations and allele loss at the RET locus in sporadic medullary thyroid carcinomas

Sporadic medullary thyroid cancer: a systematic review and meta-analysis of clinico-pathological and mutational characteristics predicting recurrence

Introduction

Sporadic medullary thyroid cancer accounts for 75% of all medullary thyroid cancers and presents at a more advanced disease stage than its hereditary counterparts. Yet there is little evidence to support risk stratification of patients according to risk of recurrence.

Methods

A systematic review and meta-analysis was performed investigating clinical and pathological factors that are associated with recurrent disease in patients with medullary thyroid cancer.

Results

10 studies totalling 458 patients were included in the meta-analyses. T3 and T4 disease (OR 9.33 (95% CI 2.5 – 34.82) p = 0.0009.), AJCC stage III and IV disease (OR 13.34 (95% CI 2.9 – 60.3) p = 0.0008) and the presence of nodal disease (OR 7.28 (95% CI 7.2–43.3) p = 0.03) were all associated with recurrent disease. RET mutations (OR 0.08 (95% CI -0.03–0.19) p = 0.17) and RET 918 T mutations (OR 1.77 (95% CI 0.804.0) P = 0.17) were not associated with disease recurrence. It was not possible to pool data with respect to extrathyroidal extension, extracapsular extension, peri-neural and lymphovascular invasion and RAS mutations.

Conclusion

T3 and T4 disease, AJCC stage III and IV disease and the presence of nodal disease are associated with recurrent disease. The heterogeneous reporting of recurrence and the lack of individual patient data precludes larger scale meta-analyses. Future research in this area should involve collaboration to establish standardised definitions of disease recurrence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13044-022-00130-8.

Utility of proGRP as a tumor marker in the medullary thyroid carcinoma

Background:

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor caused by a malignant transformation in the parafollicular C-cells of the thyroid, where calcitonin (CT) is released. Nowadays the main tumor markers (TM) used in the diagnosis and follow-up of MTC patients are CT and carcinoembryonic antigen (CEA). Nonetheless, progastrin releasing peptide (proGRP) has been recently proposed as a TM useful in the MTC. Our aims were to investigate the release of proGRP in thyroid tumors, its role in the assessment of advanced MTC and its utility in the differential diagnosis between MTC and non-MTC thyroid tumors.

Methods:

Serum samples from 22 patients with MTC and 16 with non-MTC were collected. Patients were classified into advanced cancer or no evidence of disease (NED). ProGRP was performed by Architect (Abbot Diagnostics), CT by Liaison (Diasorin) and CEA by Cobas E601(Roche Diagnostics).

Results:

ProGRP median concentration in advanced MTC was significantly higher (1398.4 pg/mL) when compared with non-MTC, either in advanced disease (24.9 pg/mL) or NED (14.6 pg/mL). In non-MTC patients, proGRP median concentration was below its cutoff level (50 pg/mL). Similar to CT, proGRP was able to detect 88.9% of MTC patients, but with a slightly lower specificity of 76.9%. Using proGRP together with CT the sensitivity increased to 100%.

Conclusions:

The low prevalence of this malignancy strongly recommends further collaborative studies, mainly focused on monitoring proGRP during tyrosine kinase inhibitors treatment for early detection of resistance and assessing its usefulness to avoid the observed false positive fluctuations that occur with CT and CEA.

Prognostic value of genetic mutations in thyroid cancer: a meta-analysis

BACKGROUND

Genetic mutations have been found to be associated with thyroid cancer. Previous studies have been focused on the relation between genetic mutations and thyroid cancer. We sought to evaluate the prognostic value of the three most common genetic mutations (BRAF, RAS, and RET) in patients with thyroid cancer.

METHODS

Sources from MEDLINE (inception to December 2013) and EMBASE (inception to December 2013) were searched. Studies of thyroid cancer with results of genetic mutations and studies that reported survival data were included and two authors performed the data extraction independently. Any discrepancies were resolved by a consensus.

RESULTS

Fourteen studies assessing BRAF mutations, 6 RAS mutations, 4 RET mutations, and 1 with analysis of both BRAF and RAS mutations were included in this meta-analysis. Patients with papillary thyroid cancer with BRAF mutations showed a 1.59-fold higher risk of events or a 2.66-fold higher risk of death than patients with papillary thyroid cancer without a BRAF mutation. Also, patients with RAS mutations showed a 2.90-fold higher risk of death by thyroid cancer than patients without a RAS mutation. In addition, patients with medullary thyroid cancer with RET mutations showed a 5.82-fold higher risk of death by the disease than without a RET mutation.

CONCLUSIONS

Genetic mutations should be considered as a poor prognostic marker in thyroid cancer and may lead to better management of individual patients. However, the use of genetic mutations as prognostic markers should not be generalized, but individualized in the specific clinic setting.

An extended family with familial medullary thyroid carcinoma and Hirschsprung's disease

Familial medullary thyroid carcinoma (FMTC) is an autosomal dominant inherited disease that has highly characteristic clinical features, including medullary thyroid carcinoma (MTC). Mutation of the RET proto-oncogene is known to be responsible for development of FMTC and for multiple endocrine neoplasia types 2A and 2B. Hirschsprung's disease is the most common form of structural intestinal obstructive disease in human newborns. Hirschsprung's disease is defined by the absence of neural crest-derived enteric ganglia along a variable length of the bowel that invariably involves the rectoanal junction. Co-segregation of FMTC and Hirschsprung's disease is uncommon; nevertheless, in 3 generations of 1 family, we observed 5 patients with FMTC, 2 patients with Hirschsprung's disease, and 1 patient with characteristics of both FMTC and Hirschsprung's disease. Moreover, a Cys620Ser mutation in RET was identified in 4 of the 8 patients. This mutation had both activating and inactivating effects on the RET (REarranged during Transfection) protein. There were individual differences in the penetrance of Hirschsprung's disease due to the RET mutation, but the penetrance of MTC was uniform and high. Genetic testing is important for making decisions about treatment and follow-up in families of this kind.

A newly identified missense mutation in RET codon 666 is associated with the development of medullary thyroid carcinoma

A 38-year-old woman with a thyroid nodule measuring approximately 2 cm was suspected to have medullary thyroid carcinoma (MTC) because of markedly elevated serum calcitonin and carcinoembryonic antigen levels. There were no signs of pheochromocytoma, whereas primary hyperparathyroidism was suspected based on the findings of inappropriate hypersecretion of parathyroid hormone although no parathyroid tumor was detected with imaging studies. RET mutation analysis revealed a novel germline missense mutation in codon 666, c.1997A>G (p.K666R). She underwent total thyroidectomy with lymphadenectomy and simultaneous total parathyroidectomy with autotransplantation of parathyroid tissue. She was given calcium lactate and alfacalcidol to prevent postoperative hypocalcemia. Pathological findings of the thyroid tumor were compatible with MTC, but the resected parathyroid glands were intact. To our knowledge, c.1997A>G (p.K666R) is a new RET mutation. This is a minor variant, but it is significant because of the possible pathogenicity in tumor formation. It is often difficult to determine whether MTC is generated as part of MEN2-related disease or familial MTC when it is a unique manifestation. In addition, it is still unclear whether all missense mutations in this codon reported previously will lead to the same clinical course and prognosis. Further careful observations of clinical presentation are required to determine the clinical features associated with this variant.

Current update on medullary thyroid carcinoma

OBJECTIVE

This article will review the multimodality imaging spectrum of medullary thyroid carcinoma (MTC) with an emphasis on anatomic and functional imaging. Recent advances in the molecular cytogenetics of this tumor and the impact on diagnosis, prognosis, and development of novel targeted therapy will be discussed.

CONCLUSION

MTC is a neuroendocrine tumor with unique clinicopathologic and radiologic features compared with other thyroid malignancies. Imaging plays an important role in the optimal management of this malignancy.

MicroRNA profiling of sporadic and hereditary medullary thyroid cancer identifies predictors of nodal metastasis, prognosis, and potential therapeutic targets

PURPOSE

While the molecular basis of hereditary medullary thyroid cancer (HMTC) has been well defined, little is known about the molecular pathogenesis of sporadic medullary thyroid cancer (SMTC). In addition, microRNAs (miRNAs) have been shown to be important diagnostic and prognostic markers in cancer but have not been defined in MTC. Our aim was to study the miRNA profile of MTC to identify prognostic biomarkers and potential therapeutic targets.

EXPERIMENTAL DESIGN

MiRNA microarray profiling was carried out in fresh frozen tissues from patients with SMTC (n = 12) and HMTC (n = 7). Differential expression of three miRNAs was confirmed in a validation cohort of SMTC and HMTC samples (n = 45) using quantitative reverse transcriptase-PCR and correlated with clinical outcomes. The functional role of a selected miRNA was investigated in vitro in the human medullary thyroid carcinoma cell line (TT cells) using cell proliferation assays and Western blotting analysis.

RESULTS

MiRs-183 and 375 were overexpressed (P = 0.001; 0.031) and miR-9* was under-expressed (P = 0.011) in SMTC versus HMTC. Overexpression of miRs-183 and 375 in MTC predicted lateral lymph node metastases (P < 0.001; P = 0.001) and was associated with residual disease (P = 0.001; 0.003), distant metastases (P = 0.003; 0.001), and mortality (P = 0.01; 0.011). Knock down of miR-183 expression in the TT cell line induced a significant decrease in the viable cell count and upregulation of the protein LC3B, which is associated with autophagy.

CONCLUSIONS

Our data indicate that miRNAs play a pivotal role in the biology of MTC and represent an important class of prognostic biomarkers and therapeutic targets warranting further investigation.

Medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) accounts for 5-8% of all thyroid cancers. MTC is mainly sporadic in nature, but an hereditary pattern [multiple endocrine neoplasia type 2 (MEN 2)] is present in 20-30% of cases, transmitted as an autosomal-dominant trait due to germline mutations of the RET proto-oncogene. About 98% of patients with MEN 2 have germline mutations in exons 5, 8, 10, 11, 13, 14, 15 or 16 of the RET gene. The primary treatment of both hereditary and sporadic forms of MTC is total thyroidectomy and removal of all neoplastic tissue present in the neck. The therapeutic option for lymph node surgery should be dictated by the results of presurgical evaluation. After total thyroidectomy, measurements of serum calcitonin (CT) and carcinoembryonic antigen are of paramount importance in the postsurgical follow-up of patients with MTC as they reflect the presence of persistent or recurrent disease. Complete remission is demonstrated by undetectable and stimulated serum CT measurement. On the contrary, if serum CT is detectable under basal conditions or becomes detectable after stimulation, the patient is probably not cured, but imaging techniques will not demonstrate any disease until serum CT approaches levels >150 pg/ml. The tumour metastasises early to both paratracheal and lateral cervical lymph nodes. Metastases outside the neck may occur in the liver, lungs, bones and, less frequently, brain and skin. Surgery is the main treatment for local and distant metastases whenever feasible. Systemic chemotherapy with dacarbazine, 5-fluorouracil and doxorubicin (alone or in combination) has shown very limited efficacy, achieving only partial responses in the range of 10-20% and of short duration. Several kinase inhibitors are currently under evaluation and preliminary results are promising. Familial cases must be identified by searching for RET proto-oncogene mutations in the proband and in family members. Carriers of the RET gene are candidates for prophylactic thyroidectomy at different ages depending on the risk associated with the specific RET mutations.

Correlation of RET somatic mutations with clinicopathological features in sporadic medullary thyroid carcinomas

Screening of REarranged during Transfection (RET) gene mutations has been carried out in different series of sporadic medullary thyroid carcinomas (MTC). RET-positive tumours seem to be associated to a worse clinical outcome. However, the correlation between the type of RET mutation and the patients' clinicopathological data has not been evaluated yet. We analysed RET exons 5, 8, 10-16 in fifty-one sporadic MTC, and found somatic mutations in thirty-three (64.7%) tumours. Among the RET-positive cases, exon 16 was the most frequently affected (60.6%). Two novel somatic mutations (Cys630Gly, c.1881del18) were identified. MTC patients were divided into three groups: group 1, with mutations in RET exons 15 and 16; group 2, with other RET mutations; group 3, having no RET mutations. Group 1 had higher prevalence (P=0.0051) and number of lymph node metastases (P=0.0017), and presented more often multifocal tumours (P=0.037) and persistent disease at last control (P=0.0242) than group 2. Detectable serum calcitonin levels at last screening (P=0.0119) and stage IV disease (P=0.0145) were more frequent in group 1, than in the other groups. Our results suggest that, among the sporadic MTC, cases with RET mutations in exons 15 and 16 are associated with the worst prognosis. Cases with other RET mutations have the most indolent course, and those with no RET mutations have an intermediate risk.

Management of medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is responsible for 13.4% of the total deaths attributable to thyroid cancer in human beings and research on MTC over the last 40 years has identified the RET proto-oncogene as a very relevant component of development of both sporadic and hereditary MTC. An activating germline RET proto-oncogene mutation responsible for a multiple endocrine neoplasia syndrome type 2 (MEN2) or a familial hereditary MTC syndrome is carried by 25% to 35% of patients with MTC. The recognition of RET proto-oncogene mutations by genetic sequencing has allowed us to differentiate hereditary from sporadic MTC, so that it is now possible to identify and treat children at risk for this disease before development of metastasis. Thanks to this discovery, we can now establish the association of MTC with other tumors in the context of MEN2 syndrome; determine adequate follow-up, prognosis, and treatment for patients with hereditary disease; and use this information to develop new therapies against both sporadic and hereditary MTCs.

Somatic mutations in the RET proto-oncogene in sporadic medullary thyroid carcinomas

The frequency and prognostic relevance of RET proto-oncogene somatic mutations in sporadic medullary thyroid carcinoma (MTC) remain controversial. In order to study somatic mutations in the RET proto-oncogene in sporadic MTCs found in the Czech population and to correlate these mutations with clinical and pathological characteristics, we investigated 48 truly sporadic MTCs by sequencing classical risk exons 10, 11, 13, 14, 15 and 16. From the 48 tumors studied, 23 (48%) had somatic mutation in the RET proto-oncogene in exons 10, 11, 15 or 16. The classical somatic mutation Met918Thr in exon 16 was only found in 13 tumors (27%). In five cases, multiple somatic mutations and deletions were detected. A statistically significant correlation between the presence of somatic mutation with more advanced pathological TNM stages was observed. Other clinical and pathological characteristics did not show any statistical significant association with the presence or absence of somatic mutation.

Prognostic significance of somatic RET oncogene mutations in sporadic medullary thyroid cancer: a 10-year follow-up study

BACKGROUND

Medullary thyroid carcinoma (MTC) is a well-differentiated thyroid tumor that maintains the typical features of C cells. An advanced stage and the presence of lymph node metastases at diagnosis have been demonstrated to be the most important bad prognostic factors. Somatic RET mutations have been found in 40-50% of MTCs. Although a relationship between somatic mutations and bad prognosis has been described, data are controversial and have been performed in small series with short-term follow ups. The aim of this study was to verify the prognostic value of somatic RET mutations in a large series of MTCs with a long follow up.

METHODS

We studied 100 sporadic MTC patients with a 10.2 yr mean follow-up. RET gene exons 10-11 and 13-16 were analyzed. The correlation between the presence/absence of a somatic RET mutation, clinical/pathological features, and outcome of MTC patients was evaluated.

RESULTS

A somatic RET mutation was found in 43 of 100 (43%) sporadic MTCs. The most frequent mutation (34 of 43, 79%) was M918T. RET mutation occurrence was more frequent in larger tumors (P=0.03), and in MTC with node and distant metastases (P<0.0001 and P=0.02, respectively), thus, a significant correlation was found with a more advanced stage at diagnosis (P=0.004). A worse outcome was also significantly correlated with the presence of a somatic RET mutation (P=0.002). Among all prognostic factors found to be correlated with a worse outcome, at multivariate analysis only the advanced stage at diagnosis and the presence of a RET mutation showed an independent correlation (P<0.0001 and P=0.01, respectively). Finally, the survival curves of MTC patients showed a significantly lower percentage of surviving patients in the group with RET mutations (P=0.006).

CONCLUSIONS

We demonstrated that the presence of a somatic RET mutation correlates with a worse outcome of MTC patients, not only for the highest probability to have persistence of the disease, but also for a lower survival rate in a long-term follow up. More interestingly, the presence of a somatic RET mutation correlates with the presence of lymph node metastases at diagnosis, which is a known bad prognostic factor for the definitive cure of MTC patients.

RET is constitutively activated by novel tandem mutations that alter the active site resulting in multiple endocrine neoplasia type 2B

Constitutive activation of the RET receptor tyrosine kinase underlies the genesis and progression of multiple endocrine neoplasia type 2 (MEN 2), a dominantly inherited cancer predisposition. Importantly, although kinase activation represents a common theme in neoplasias, not all activating mutations are functionally equivalent. Consistent with this, we ascertained a patient with classical features of MEN 2B, but lacking either of the classical mutations in RET (M918T or A883F). Instead, the patient harbors a novel pair of germ line missense mutations in cis at codons 804 and 805. We evaluated the potential physiochemical effects of these substitutions in silico, predicting both to be moderately deleterious in isolation, but severely deleterious in combination. Consistent with this postulate, we show that the identified tandem mutations (V804M/E805K) are biologically active, transforming cells in culture and that their transforming capacity in combination is distinctly synergistic. Furthermore, the V804M/E805K tandem lesion confers resistance to the small molecule receptor tyrosine kinase inhibitor, PP1, suggesting a mode of action distinct from that known for classical MEN 2B mutations. To address this question, we used homology molecular modeling in silico to model the active site of RET. We predict that RET804 constitutes a critical gatekeeper residue that, when mutated in combination with RET805, induces a conformational change in the hinge region that locks the active site in a position permissive for ATP hydrolysis. Our findings have implications both in the clinic and in the successful development of novel kinase-targeted anticancer drugs.

Structure and chemical inhibition of the RET tyrosine kinase domain

The RET proto-oncogene encodes a receptor tyrosine kinase for the glial cell line-derived neurotrophic factor family of ligands. Loss-of-function mutations in RET are implicated in Hirschsprung disease, whereas activating mutations in RET are found in human cancers, including familial medullar thyroid carcinoma and multiple endocrine neoplasias 2A and 2B. We report here the biochemical characterization of the human RET tyrosine kinase domain and the structure determination of the non-phosphorylated and phosphorylated forms. Both structures adopt the same active kinase conformation competent to bind ATP and substrate and have a pre-organized activation loop conformation that is independent of phosphorylation status. In agreement with the structural data, enzyme kinetic data show that autophosphorylation produces only a modest increase in activity. Longer forms of RET containing the juxtamembrane domain and C-terminal tail exhibited similar kinetic behavior, implying that there is no cis-inhibitory mechanism within the RET intracellular domain. Our results suggest the existence of alternative inhibitory mechanisms, possibly in trans, for the autoregulation of RET kinase activity. We also present the structures of the RET tyrosine kinase domain bound to two inhibitors, the pyrazolopyrimidine PP1 and the clinically relevant 4-anilinoquinazoline ZD6474. These structures explain why certain multiple endocrine neoplasia 2-associated RET mutants found in patients are resistant to inhibition and form the basis for design of more effective inhibitors.

New multiple somatic mutations in the RET proto-oncogene associated with a sporadic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) occurs mostly as a sporadic tumor or in connection with inherited cancer syndromes-multiple endocrine neoplasia (MEN) types 2A and 2B and familial MTC. Germline mutations in the RET proto-oncogene are found in most of the familial cases. Somatic mutations in the RET proto-oncogene are detected in 23%-69% of patients with sporadic MTC. The most frequent somatic mutation is Met918Thr in exon 16 and only a small percentage of mutations in other RET exons have been observed. In a very few cases double mutations were found. Genetic screening for somatic mutations in RET exons 10, 11, 13, 14, 15, and 16 in Czech patients with sporadic MTC was carried out by DNA sequencing. This study presents a new triplesomatic mutation Gly911Asp, Met918Thr, and Glu921Lys in exon 16 of the RET proto-oncogene detected in an 18-year-old Czech male patient. In the second case, a new double-somatic mutation Val591Ile in exon 10 with a concomitant somatic mutation Met918Thr in exon 16 was found in a 77-year-old Czech female patient. These both newly described somatic multiple mutations were revealed in a hemizygous status, the loss of heterozygosity in tumor tissues in comparison with germline DNA was confirmed.

Analysis of inherited genetic variants in ret proto-oncogene of Brazilian patients with apparently sporadic medullary thyroid carcinoma

Mutations in different exons of ret proto-oncogene are responsible for the development of medullary thyroid carcinoma (MTC). The mutations can occur as sporadic or as part of multiple endocrine neoplasia (MEN) type 2 hereditary syndromes. Here we report the first focused study of sporadic MTC in Brazilian patients regarding clinical and molecular analysis of ret proto-oncogene. Our study seeks to estimate the risk of hereditary MTC cases among apparently sporadic cases in a Brazilian population and describe ret genetic variants in their germinative lineage. Germinative sequence variants were screened by DNA sequencing and denaturing gradient gel electrophoresis (DGGE) analysis of exons 10, 11, 13, 14, 15, and 16 of 24 Brazilian patients with apparently sporadic MTC. We identified 1 inherited case of 24 (4%) patients with apparently sporadic MTC. Polymorphisms for the ret proto-oncogene coding region were identified in codon 769 of exon 13 (LeuCTT--> LeuCTG) at a frequency of 13% (3/24) and in codon 904 of exon 15 (SerTCC--> SerTCG) at a frequency of 16.6% (4/24). The observed frequency (4%) of inherited disease among apparent sporadic MTC strengthens routine application of ret proto-oncogene germinative DNA screening in all cases of apparently sporadic MTC ascertained at Brazilian cancer hospitals.

The newly detected mutations in the RET proto-oncogene in exon 16 as a cause of sporadic medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) occurs as a sporadic form or, less frequently, as an autosomal dominant inherited familial disorder. Germline mutations in the RET proto-oncogene in exons 10, 11, 13, 14, 15, and 16 are found in most of the familial cases (nearly 95%). Somatic mutations in sporadic MTC are detected in 23-69% of patients. The most frequent somatic mutation is located in exon 16 at codon 918, and only a small percentage of mutations are found in exons 10, 11, 13, and 15. We have searched for somatic mutations in Czech MTC patients using direct sequencing. We report here two new somatic missense mutations in exon 16 of the RET proto-oncogene associated with the sporadic MTC detected in two Czech men. A homozygous mutation at codon 922 TCC(Ser)-->CCC(Pro) as a result of loss of heterozygosity was revealed in the first patient. In the second one a heterozygous mutation at codon 930 ACG(Thr)-->ATG(Met) was found.

Allelic loss of DNA locus of the RET proto-oncogene in small cell lung cancer

We analyzed all 21 exons of the RET proto-oncogene of paired genomic DNA from tumors and normal tissues in 12 small cell lung cancer (SCLC) patients for the presence of genetic alteration. Polymerase chain reaction single-strand conformation polymorphism analysis and direct sequencing revealed that heterozygosity of the RET proto-oncogene was lost in the tumor tissues of six patients out of eight informative SCLC patients, although point mutation was not evident in any tumors. These results suggest that a deletion of the chromosomal region including the RET proto-oncogene is involved in the pathogenesis of SCLC.

The finding of a somaticdeletion in RET exon 15 clarified the sporadic nature of amedullary thyroid carcinoma suspected to be familial

Medullary thyroid carcinoma (MTC) occurs both sporadically and in the autosomal dominantly inherited multiple endocrine neoplasia (MEN) type 2 syndromes. The distinction between both is important for future clinical management. We report a family initially described as a familial MTC by pentagastrin stimulation test and clinical outcome, in which we found a 12 bp deletion within the catalytic domain of the protooncogene RET in the index case tumor alone. Linkage study suggests that it is a sporadic MTC. Therefore, in view of these results, in kindred with just one MTC case, borderline pentagastrin test values must be carefully assessed. In addition, this and other mutations can help us to understand some features about domains that play an important role in the normal function of this tyrosine kinase receptor and involved in MTC.

Large-scale analysis of mutations in RET exon 16 in sporadic medullary thyroid carcinomas in Japan

Germline mutations in the RET proto-oncogene are the cause of multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Some cases of sporadic medullary thyroid carcinoma (MTC) have also been reported to have mutations in the RET gene. However, two previous reports have given discrepant results on the frequency of the mutations in RET in sporadic MTCs in Japan. To clarify this problem, we analyzed mutations in RET exon 16 in 72 sporadic MTCs by means of the two methods used in the previous studies, direct sequencing and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Mutations in exon 16 were detected in only 2 of 72 cases of sporadic MTC. These results suggest that when a MTC has a mutation in RET exon 16, it is more likely to be a hereditary MTC than a sporadic one in Japan.

Estimation of risk of inherited medullary thyroid carcinoma in apparent sporadic patients

PURPOSE

The study was undertaken to evaluate the frequency of inherited medullary thyroid carcinoma (MTC) among patients with apparent sporadic disease. A stepwise algorithm was used depending on clinical indices and the age of patient at MTC diagnosis.

PATIENTS AND METHODS

One hundred sixteen patients with MTC verified by postoperative pathologic examination were subjected to genetic analysis of RET exons 10, 11, 13, 14, and 16 by means of polymerase chain reaction, restriction endonuclease digestion, and DNA sequencing.

RESULTS

Among 116 apparent sporadic MTC patients, we identified eleven (9.5%) RET germline mutation carriers. Seven of these (6.0%) were found by routine analysis (exons 10 and 11). The frequency of inherited disease among patients younger than 45 years at diagnosis was 10.2% by analysis of typical mutations in exons 10 and 11. Extended genetic analysis (sequencing of exons 11, 13, 14, and 16) yielded 6.1% additional diagnoses, giving a risk of 16.3% in this age group. One previously unreported mutation in exon 11 affected codon 649 (TCG>TTG, Ser>Leu). In the true sporadic MTC patients younger than 30 years at diagnosis, frequencies of 36% and 4.5% in polymorphic variants L769L and S836S, respectively, were observed. The frequency for L769L was higher than in older patients (P <.05).

CONCLUSION

The frequency of inherited disease among apparent sporadic medullary thyroid carcinoma patients is close to 10% in the Polish population of MTC patients. The extended analysis of all known RET proto-oncogene mutation sites is obligatory in patients younger than 45 years at diagnosis, but we also see the need to analyze the impact of rarer mutations in older patients.

Multiple endocrine neoplasias

The multiple endocrine neoplasia syndromes form a distinct group of genetic tumor syndromes. They include multiple endocrine neoplasia types 1 and 2, von Hippel Lindau syndrome, neurofibromatosis, and Carney complex. Research over the past decade has identified a molecular basis for each of these syndromes. This knowledge has revolutionized not only the clinical management but also has illuminated the field of human cancer research by the identification of new and important genes critical for regulation of cell growth, differentiation, and death. This review focuses on the structure, physiologic function, and molecular abnormalities of the genes involved in these syndromes.

Somatic mutations in RET exons 12 and 15 in sporadic medullary thyroid carcinomas: different spectrum of mutations in sporadic type from hereditary type

Germline mutations in the RET proto-oncogene are responsible for multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Point mutations or in-frame deletions of exons 10, 11, 13, 14 and 16 are associated with sporadic medullary thyroid carcinoma (MTC). To understand further the role of the RET gene in sporadic MTC, we examined mutations in exons 12 and 15 of RET in patients with sporadic MTC. DNAs were extracted from 39 formalin-fixed tumor tissues and corresponding normal thyroid tissues or peripheral blood leukocytes. DNA sequencing was used to identify mutations in exons 12 and 15 of RET. In this study, one novel somatic mutation was found in exon 12 and five novel mutations or deletions were found in exon 15. Of the patients with mutations, one had an in-frame 12-bp deletion (nt. 2625-2636), one had point mutations in both codons 884 and 908, and the remaining three had point mutations in codons 748, 876 and 901, respectively. Together with our previous identification of somatic mutations in exons 10, 11, 13, 14 and 16, somatic alterations were found in 10 out of 39 (25.6%) sporadic MTCs. There was no association of RET gene mutations with tumor recurrence or prognosis. These results suggest that mutations occur frequently in the RET coding region in addition to the previously reported mutation hot spots, and there is a different spectrum of mutations between sporadic and hereditary MTC.

Presymptomatic detection and treatment of Japanese carriers of the multiple endocrine neoplasia type 2A gene

DNA extracted from the peripheral blood leukocytes of 36 members of five families with multiple endocrine neoplasia (MEN) type 2A was analyzed for mutations of exons 10, 11, 13, 14, and 16 of the RET proto-oncogene by nonisotopic polymerase chain reaction-single-strand conformation polymorphism analysis and automated DNA sequencing. Germline mutations were found in all 9 of the affected individuals and in 6 of the 27 individuals of unknown status. A 70-year-old man who had been completely asymptomatic before genetic diagnosis underwent left adrenalectomy and total thyroidectomy, and was found to have pheochromocytoma and multifocal micromedullary thyroid carcinoma (MTC). A 32-year-old man and a 15-year-old boy, with elevated calcitonin levels detected by the C-cell-stimulation test, but no evident thyroid tumor, underwent total thyroidectomy. Histopathological diagnosis revealed multiple micro MTCs. A 7-year-old girl without evidence of a thyroid tumor or an elevated calcitonin level is being followed up. The remaining two subjects with an evident thyroid tumor and elevated calcitonin levels refused surgery. These results suggest that genetic screening for MEN type 2 afflicted family members can facilitate the presymptomatic detection of gene carriers. Thus, we must carefully evaluate whether immediate prophylactic total thyroidectomy is indicated for gene carriers of MEN 2A without an evident thyroid tumor or elevated calcitonin levels.

Loss of heterozygosity in human skin

Loss of heterozygosity (LOH) is a genetic mechanism by which a heterozygous somatic cell becomes either homozygous or hemizygous because the corresponding wild-type allele is lost. LOH has today been recognized as a major cause of malignant growth. This article gives a comprehensive review of skin disorders in which an origin from LOH has been either documented at the molecular level or postulated on the basis of clinical evidence. LOH has been shown to cause basal cell carcinoma, squamous cell carcinoma, and malignant melanoma, but this mechanism can likewise be taken as an important model to explain the origin of many other skin diseases such as benign hamartomas; type 2 segmental manifestation of autosomal dominant skin disorders; a pronounced segmental manifestation of acquired skin disorders with a polygenic background, superimposed on symmetric lesions of the usual type; paired mutant patches in the form of either allelic or nonallelic twin spotting; and the exceptional familial occurrence of some nevi, reflecting paradominant transmission. completion of this learning activity, readers should be familiar with the mechanism of LOH and its general significance for the biology of plants, animals, and humans. Participants should understand that this mechanism plays a crucial role not only in cutaneous malignant growth but also in the development of benign skin disorders, and they should be able to examine such diseases with a prepared mind to gain a better understanding of their origin.

Two germline missense mutations at codons 804 and 806 of the RET proto-oncogene in the same allele in a patient with multiple endocrine neoplasia type 2B without codon 918 mutation

Multiple endocrine neoplasia (MEN) type 2B is a clinically distinct entity among the autosomal dominant MEN 2 syndromes. Most patients with MEN 2B carry a germline mutation (M918T) of the RET proto-oncogene, while a few carry A883F. We examined a patient with MEN 2B, but without M918T or A883F, and her relatives. Here, we report the presence in this patient of 2 germline mutations, V804M and Y806C in the same allele. While the novel Y806C was inherited from her father, its carriers (her father and brother) was not affected by MEN 2. In contrast, V804M was a de novo mutation, that has been reported in patients with familial medullary thyroid carcinoma. Combinations of mutations of the RET proto-oncogene may cause oncogenic activities different from those of single mutations.