Prediction of affected MEN2A gene carriers by DNA linkage analysis for early total thyroidectomy: a progress in clinical screening program for children with hereditary cancer syndrome

Review of multiple endocrine neoplasia type 2A in children: therapeutic results of early thyroidectomy and prognostic value of codon analysis

OBJECTIVES

The aim of this study was first to investigate whether early total thyroidectomy (ETT; 1-5 years of age) can prevent medullary thyroid carcinoma with persistent or recurrent disease (PRD) in pediatric patients with multiple endocrine neoplasia type 2A (MEN-2A) and second, to evaluate the strength of codon analysis in children with MEN-2A as prognostic parameter.

METHODS

Case reports and review of the literature for pediatric patients with MEN-2A were conducted. Inclusion criteria were age (0-20 years) and histologic degree of C-cell disease (normal = N, C-cell hyperplasia = CCH, medullary thyroid carcinoma = MTC, metastatic MTC = MMTC). To evaluate therapeutic results of ETT (1-5 years) versus late total thyroidectomy (LTT; 6-20 years), age-dependent histologic stages of C-cell disease and postoperative occurrence of PRD were compared. Prognostic value of specific codons, age-dependent histologic distribution, and long-term outcome were analyzed.

RESULTS

In a total of 260 cases, 42 (16%) underwent ETT, and 218 (84%) underwent LTT. Histologic analysis showed significant difference between ETT versus LTT (57% vs 76%) regarding malignant stage of C-cell disease (of combined rate of MTC and MMTC). Long-term outcome was documented in 74 patients (28%). During a median follow-up period of 2 years (range: 0-15 years), 21 of 65 of the LTT group versus 0 of 9 of the ETT group suffered PRD. Information about codon analysis was available in 150 patients (58%). Mutated codons were c634 (63%), c618 (19%), c620 (9%), and c804 (6%). Codon-related histologic analysis resulted in prognostic differences: 81% of patients with c634-mutation had MCT or MMTC in contrast to c804 (44%), c618 (34%), and c620 (7%). Fifteen of 17 MMTC and 7 of 9 PRD occurred in patients with c634-mutation.

CONCLUSIONS

1) ETT until 5 years of age in MEN-2A gene carriers results in significant reduction of MTC and MMTC in favor of CCH and improved disease-free long-term outcome. 2) Codon analysis is an important prognostic factor. Timing of TT could be individualized based on codon-specific prognosis. Until more detailed knowledge is available, consequent genetic and biochemical screening is mandatory for appropriate individual timing of ETT before age of 5 years.

Germline mutations of the RET proto-oncogene in pedigree with MEN type 2A: DNA analysis and its implications for pediatric surgery

To assess the feasibility of screening for multiple endocrine neoplasia type 2A (MEN 2A), the authors used DNA sequence analysis to evaluate the RET proto-oncogene in a kindred with MEN 2A. The kindred consisted of 95 members (1 to 79 years of age) and their spouses, and spanned five generations. Genomic DNA was extracted from peripheral blood lymphocytes or lymphoblastoid cell lines established from the family members, and the RET gene was amplified by polymerase chain reaction (PCR) using RET-specific primers (10q 11.2) and was sequenced. Periodic endocrine screening also was performed, by measuring the plasma calcitonin concentration after provocation with pentagastrin (0.5 microgram/kg intravenously) to assess its reliability for detecting the associated neoplasms. Nineteen patients were confirmed to have MEN 2A by medical records or the screening program. The DNA sequence of the PCR products from clinically established MEN 2A patients showed a mutation at codon 634 (TGC-->CGC) that resulted in an amino acid change from cysteine to arginine. Endocrine screening tests showed that six other family members had a mutated RET protooncogene. DNA sequencing can detect high-risk cases at a preclinical stage of the disease. The establishment of mutated MEN 2A gene carriers allows pediatric surgeons to consider total thyroidectomy at a very early stage of neoplasm development (C-cell hyperplasia) or even prophylactically.

Physiologic versus neoplastic C-cell hyperplasia of the thyroid: separation of distinct histologic and biologic entities

BACKGROUND

Although hyperplasia of C-cells has been described in association with various pathologic and physiologic conditions, criteria for its diagnosis are poorly defined. Both neoplastic and physiologic C-cell proliferations have been lumped together under the umbrella designation of C-cell hyperplasia (CCH), creating considerable confusion among clinicians and pathologists.

METHODS

in order to compare the morphologic and immunohistochemical characteristics of the two major types of CCH, we examined thyroid sections of 17 patients with familial forms of C-cell hyperplasia and/or neoplasia and tissue sections of 19 thyroid glands known to have reactive or physiologic CCH (at least 50 C-cells per one low power field, 100X). Hematoxylin and eosin (H & E) stained sections and immunohistochemical stains for calcitonin were assessed in each case.

RESULTS

Physiologic or reactive CCH was not recognized with certainty on H & E stains in any of the cases due to morphologic similarities between C-cells and adjacent follicular cells. Detection of this form of hyperplasia, which was predominantly diffuse, required calcitonin immunostains and quantitative analysis. Conversely, nodular and diffuse neoplastic CCH was easily identified with conventional H & E stains at the periphery of 11/12 (92%) familial medullary thyroid carcinomas (MTC). In the other five cases, neoplastic C-cell hyperplasia was the only pathologic finding on thyroidectomy performed for elevated serum calcitonin levels detected via provocative biochemical screening or identification of the mutated RET proto-oncogene by genetic analysis. The C-cells in this neoplastic form of CCH were large, mildly to moderately atypical, and confined within the basement membrane of thyroid follicles. Moreover, these cells were cytologically indistinguishable from those of invasive MTC cells.

CONCLUSIONS

Physiologic and neoplastic CCH are biologically and morphologically distinct entities. The former cannot be recognized with certainty with conventional stains and requires immunohistochemistry and quantitative analysis for diagnosis. The latter consists of mildly to moderately atypical C-cells that can be identified with H & E stained sections. Consequently, the number of C-cells is of no importance for the diagnosis of neoplastic CCH which is considered to be the precursor (medullary carcinoma in situ) of invasive medullary carcinoma.