RET is expressed but not mutated in extra-adrenal paragangliomas

Genetic aberrance of sporadic MEN 2A component tumours: analysis of RET

AIM

The molecular pathogenesis of familial multiple endocrine neoplasia (MEN) type 2 (parathyroid adenoma with medullary thyroid carcinoma and adrenal pheochromocytoma) is associated with a germ-line mutation in the RET proto-oncogene. We undertook this study to clarify the relationship between the tumorigenesis of apparently sporadic MEN type 2 component endocrine tumours and RET mutations.

METHODS

Direct sequencing for RET exon 10, 11, 12, 13, 14, 15 and 16 and immunohistochemistry for RET monoclonal antibody were performed on the archival tissues of 84 cases of sporadic endocrine tumours, including 22 medullary thyroid carcinomas (MTCs), 35 adrenal pheochromocytomas (APCs), 18 paragangliomas (PGs), and nine parathyroid adenomas (PTAs).

RESULTS

PCR-based direct sequencing revealed somatic point missense mutation within 22.7% of exon 13 of the RET proto-oncogene (four cases of E768D, one case of S7781) in MTCs. No RET genotype and morphological association was observed in MTCs or APCs. APCs revealed significantly lower levels of immunoexpression of RET, even versus PGs.

CONCLUSIONS

The genetic mutation in RET is relatively low in incidence, and likely to play an insignificant role in the molecular pathogenesis of sporadic MTC. The molecular bases of PG and APC seem to be different despite their embryological and histological similarities.

Familial paraganglioma and gastric stromal sarcoma: a new syndrome distinct from the Carney triad

Paragangliomas may be inherited in an autosomal dominant manner either alone (as in PGL1, PGL2, and PGL3 syndromes) or as a component of a multiple tumor syndrome (as in von Hippel-Lindau disease and neurofibromatosis type 1). In this article, we describe 12 patients (7 male and 5 female) with an average age of 23 years from five unrelated families that manifested paraganglioma and gastric stromal sarcoma; the tumors were inherited in an apparent autosomal dominant manner, with incomplete penetrance. Seven patients had paraganglioma, four had paraganglioma and gastric stromal sarcoma, and one had gastric stromal sarcoma. The paraganglioma was multicentric and the gastric stromal sarcoma multifocal. Because of the rarity of gastric stromal sarcoma and its multifocality, the young age of the patients, and the unlikelihood of coincidental co-occurrence of paragangliomas and gastric stromal sarcomas, we suggest that a new syndrome exists with these two main components, a condition that is familial and distinct from the Carney triad.

The RET proto-oncogene in human cancers

The activation of the RET proto-oncogene contributes to the development of human cancers in two different ways. Somatic rearrangements of RET with a variety of activating genes, which contribute to unscheduled expression and constitutive dimerization of the chimeric RET/PTC oncoproteins in thyroid follicular cells, are frequently found in radiation-induced papillary thyroid carcinomas. Germ-line mutations, mainly point mutations, that lead to constitutive activation of RET tyrosine kinase activity are responsible for the development of the inherited cancer syndrome, multiple endocrine neoplasia type 2. There appears to be a correlation between specific types of RET mutation and clinical phenotypes of the cancers involved. The biological effects and the signaling pathways induced by different forms of RET activation have been investigated in a variety of cultured cells as well as in genetically engineered animal models. The identification of RET mutations in most MEN 2 families (95%) has translated into improved care for MEN 2 patients. However, further investigation of the signaling pathways contributing to tumorigenesis in relevant tissues will eventually help us to develop novel strategies to prevent or to treat human papillary thyroid carcinomas, MEN 2 disease, as well as the sporadic cancers relevant to MEN 2 disease.