C-Cells and their Associated Lesions and Conditions: A Pathologists Perspective.

This paper updates the histopathology and cytopathology of thyroid tumors and proliferations derived from the para-follicular or C cells. Beginning with an historical over view, including the recognition of medullary thyroid carcinoma as a distinct histologic entity, its relationship to the hormone, calcitonin, (which was discovered in the same decade) and to thyroid C cells, medullary carcinoma and its variants are reviewed. The molecular biology of the tumors and the associated mutations in the tumors (somatic mutations) are discussed. Additionally the genetic features (germline mutations) including familial clusters and associations with other endocrine and neuroendocrine lesions are reviewed. Screening for the tumor and its precursors is included with a review of the latest American Thyroid Association guidelines for treatment as well as timing and approach to surgery. Tabular data of specific germline mutations and their relationships to tumor virulence, and prognosis are illustrated. Precursor and early C cell lesions such as C-cell hyperplasia and micro-medullary carcinoma are discussed. Difficulties and controversies in the definition of C-cell proliferations which are neoplastic and those which are "reactive" are reviewed. The entity of medullary microcarcinoma or medullary microcarcinoma is illustrated and the distinction between C cell nodules and microcarcinoma is defined using the latest available criteria. Finally the latest approved chemotherapeutic agents and their results in metastatic medullary thyroid carcinoma are included.

A case of multiple endocrine neoplasia type II accompanied by thyroid medullary carcinoma and pheochromocytomas expressing corticotropin-releasing factor and urocortins.

A 38-year-old woman with RET gene mutation presented with tumors in her thyroid and bilateral adrenal glands. I-metaiodobenzylguanidine scintigraphy revealed accumulation of the radioisotope in both adrenal glands. Both plasma adrenaline and noradrenaline levels were elevated. The circadian rhythms for plasma adrenocorticotropic hormone (ACTH) and cortisol levels were disturbed. Plasma ACTH and cortisol levels failed to be suppressed by an overnight dexamethasone test, suggesting autonomic secretion of ACTH and cortisol, although the patient had no typical Cushingoid features, hypertension, or impaired glucose tolerance. Pathological examination showed that these tumors were pheochromocytoma and thyroid medullary carcinoma, respectively, both of which highly expressed corticotropin-releasing factor, urocortin1, and urocortin3. Together with the endocrinological and pathological observations, the patient was diagnosed as multiple endocrine neoplasia type II with corticotropin-releasing factor- and urocortin-producing tumors that stimulated ACTH and glucocorticoid secretion.

Neuropeptide Y expression in phaeochromocytomas: relative absence in tumours from patients with von Hippel-Lindau syndrome.

Phaeochromocytomas are rare neuroendocrine tumours that produce catecholamines and numerous secretory proteins and peptides, including neuropeptide Y (NPY), a vasoactive peptide with influences on blood pressure. The production of catecholamines and NPY by phaeochromocytomas is highly variable. This study examined influences of hereditary factors and differences in catecholamine production on tumour expression of NPY, as assessed by quantitative PCR, enzyme immunoassay and immunohistochemistry. Phaeochromocytomas included hereditary adrenaline-producing tumours (adrenergic phenotype) in multiple endocrine neoplasia type 2 (MEN 2), predominantly noradrenaline-producing tumours (noradrenergic phenotype) in von Hippel-Lindau (VHL) syndrome, and other adrenergic and noradrenergic tumours where there was no clear hereditary syndrome. NPY levels in phaeochromocytomas from VHL patients were lower (P<0.0001) than in those from MEN 2 patients for both mRNA (84-fold difference) and the peptide (99-fold difference). These findings were supported by immunohistochemistry. NPY levels were also lower in VHL tumours than in those where there was no hereditary syndrome. Relative absence of expression of NPY in phaeochromocytomas from VHL patients when compared with other groups appears to be largely independent of differences in catecholamine production and is consistent with a unique phenotype in VHL syndrome.

Ret protein expression in adrenal medullary hyperplasia and pheochromocytoma.

Ret is a developmentally regulated tyrosine kinase involved in formation and maintenance of the nervous system. Ret mutations predisposing to pheochromocytomas and medullary thyroid carcinomas occur in multiple endocrine neoplasia (MEN) syndromes 2A and 2B. Biochemical studies have demonstrated overexpression of Ret mRNA and protein in pheochromocytomas compared to normal adrenal medulla. However, the cellular distribution of Ret in the normal human adrenal and in hyperplastic lesions that antecede pheochromocytomas are unclear. The present investigation was undertaken to resolve the histological distribution of Ret in the normal human adrenal, in pheochromocytomas evolving from adrenal medullary hyperplasia in MEN2A and in sporadic pheochromocytomas. Ret expression was studied by immunohistochemistry using both a polyclonal and a monoclonal antibody, with confirmation by immunoblotting of representative cases. Only occasional cells stained for Ret in the normal adrenal, consistent with the distribution in adult adrenals of other species. Heterogeneous, progressively increased Ret expression was observed during the evolution of pheochromocytomas. In both normal and neoplastic adrenal, the most intense immunoreactivity was observed in cells with neuron-like features. Our finding that Ret is not expressed at high levels in the early stages of disease suggests that elucidation of mechanisms that regulate Ret expression is required for understanding the pathobiology of MEN2A. The association of high-level Ret expression with neuronal morphology suggests that the variable overexpression of Ret in pheochromocytomas might in part be an epiphenomenon, reflecting the known phenotypic plasticity of these tumors.

Simultaneously occurring liver metastases of pheochromocytoma and medullary thyroid carcinoma--a diagnostic pitfall with clinical implications for patients with multiple endocrine neoplasia type 2a.

Malignant pheochromocytoma is an exceptional complication in patients with Multiple Endocrine Neoplasia Type 2a (MEN2a). In this paper, we report on a 53-year-old male patient with an evident RET gene germline mutation, who simultaneously developed hepatic metastases of medullary thyroid carcinoma (MTC) and pheochromocytoma. Comprehensive immunohistochemical investigations were performed to elaborate markers which could be useful for differentiating between MTC metastases and pheochromocytoma, respectively. Calcitonin and CEA, in particular cytokeratins and trefoil factor family 1 (TFF1), were detectable exclusively in MTC, whereas all the other markers revealed a comparable expression in both MTC and pheochromocytoma. The only clues that could indicate a potential malignant course were size, a lack of sustentacular cells and hyaline globules, and a focal spindle cell pattern in pheochromocytoma. Owing to a wide agreement in cellular differentiation and a lack of specific, routinely applicable markers for pheochromocytomas, a comprehensive and goal-directed immunohistochemistry is required to rule out pheochromocytoma metastasis in patients with MEN2a. A misinterpretation could lead to harmful clinical complications, as shown in the present case.

Detection of ret homodimers in MEN 2A-associated pheochromocytomas.

Using transfection of NIH 3T3 cells, we have recently demonstrated that multiple endocrine neoplasia (MEN) 2A mutations activate the c-Ret protein by inducing its disulfide-linked homodimerization on the cell surface. To investigate whether the homodimers are present in original tumors, the expression of the c-Ret protein was analyzed in eight sporadic and two MEN 2A-associated pheochromocytomas, the latter two of which contained mutations in cysteine 618 or 634 of Ret. The c-Ret protein was expressed at variable levels in all pheochromocytomas examined. By labeling the c-Ret protein immunoprecipitated from tumor tissues with [gamma-32P]ATP in vitro, its homodimers were detected in pheochromocytomas from MEN 2A patients but not in a sporadic tumor. This result represents the first demonstration of Ret homodimers in original tumors.

Immunostains for collagen type IV discriminate between C-cell hyperplasia and microscopic medullary carcinoma in multiple endocrine neoplasia, type 2a.

At a light microscopic level, the separation of C-cell hyperplasia and microscopic medullary carcinoma of the thyroid (MCT) is difficult, and it ultimately rests on the finding of C cells outside of the thyroid follicular basement membranes (FBMs). To date, this has required ultrastructural examination for proper documentation. The assessment of thyroidectomy specimens from patients with multiple endocrine neoplasia, type 2a (MEN2a), a hereditary condition in which there is widespread C-cell hyperplasia (CCH) and multifocal MCT, presented an opportunity to the authors to assess the entire range of C-cell abnormalities. Total thyroidectomy specimens from 17 patients with MEN2a were examined. In addition to hematoxylineosin (H&E) stains, representative tissue sections were labeled for chromogranin A and collagen type IV (CIV), using the avidin-biotin-peroxidase complex (ABC) method. All patients in the study had multifocal C-cell proliferation that was both diffuse and nodular. Fifteen had microscopic MCTs, which were multifocal in eight instances. Three patterns of C-cell proliferation were recognized in CIV immunostains. The first was characterized by complete investment of C-cells by a continuous rim of CIV, corresponding to FBM and confirming an intrafollicular localization; hence, the diagnosis of CCH was made in such cases. The second pattern was distinctive and was typified by defects in the CIV layer; constituent C-cells assumed an extrafollicular location. These images yielded a diagnosis of micro-MCT. The latter findings were also accompanied by focal reduplication of basement membrane that was apparently tumor derived, producing a micronodular or microlobular configuration. The third pattern represented a combination of the first two, with C-cell nodules that were bounded by CIV and clearly situated in an intrafollicular location; however, focal reduplication of basement membranes was also evident in these cases. The biological significance of the third pattern of CIV staining is uncertain, but it may reflect the presence of a preinvasive proliferation of C-cells that is distinct from "usual" CCH in MEN2a.