[Medullary thyroid carcinoma]

[Hereditary medullary thyroid cancer]

Parafollicular C cells progress via C cell hyperplasia to medullary thyroid cancer (MTC), which can be present even in the first years of life in multiple endocrine neoplasia (MEN) type 2A and 2B patients. Basal calcitonin and carcinoembryonic antigen (CEA) are useful tumor markers for the diagnosis and monitoring. The prognosis depends on the stage when the disease is diagnosed and there is a good genotype-phenotype correlation with the RET proto-oncogene, which can be used for estimation of the risk. The risk-stratified prophylactic thyroidectomy plays a decisive role in the prognosis of known gene mutation carriers.

[Functional diagnostics in endocrinology]

When investigating many endocrinological diseases, basal laboratory parameters are not sufficient to distinguish between physiological and pathological hormone secretion. Functional diagnostics plays a decisive role in this context. Stimulation and suppression tests are used depending on whether under- or over-function needs to be diagnosed. This review article discusses selected functional tests, each of which plays an important role in current guidelines. Indications and test principles, including their performance, reliability, and limitations, are discussed. Topics covered include the ACTH stimulation test for the diagnosis of adrenal cortex insufficiency and the dexamethasone inhibition test for suspected Cushing's syndrome, as well as functional tests for the diagnosis of primary hyperaldosteronism, pheochromocytoma, acromegaly, growth hormone deficiency, thyroid nodules and suspicion of medullary thyroid carcinoma, insulinoma, and Zollinger-Ellison syndrome. Functional tests that are explicitly not recommended are also addressed.

[Genetics of thyroid nodules and thyroid carcinoma]

Thyroid nodules are heterogeneous tumors with variable genetic signatures. Thyroid cancers are monoclonal lesions with a defined histomorphology that largely depends on the underlying somatic mutation. While the mutation rate is generally low in differentiated thyroid cancers, poorly differentiated and anaplastic thyroid cancers show a high mutation load. The identification of somatic mutations in fine needle aspirates can be helpful for the differential diagnostics of thyroid nodules; however, a prognostic contribution is less certain. The molecular pathology of thyroid tumors is helpful for the development of targeted therapies and may infer novel immuno-oncological concepts for advanced aggressive thyroid cancers.

How to Assess the Clinical Relevance of Novel RET Missense Variants in the Absence of Functional Studies?

INTRODUCTION AND BACKGROUND

Familial medullary thyroid cancer (FMTC) is caused by gain of function mutations in the proto-oncogene RET (rearranged during transfection). Missense mutations within exon 14 including p.Val804Met are known to cause FMTC and multiple endocrine neoplasia type 2a/b. The clinical significance of other novel missense variants within this hotspot region of exon 14 is not delineated.

CASE DESCRIPTION

A three-generation pedigree of FMTC is presented with the co-occurrence of two missense variants within exon 14 of the RET gene, the known variant p.Val804Met and the novel variant p.Val826Met. The female index patient developed medullary thyroid cancer at the age of 42 years and was heterozygous for both missense variants. Her younger sister was also tested to be compound heterozygous for both mutations, and five further relatives were heterozygous for only one of both sequence variants. Prophylactic thyroidectomy was recommended for the two carriers of the RET mutation p.Val804Met, revealing a C-cell hyperplasia for one of them at the age of 19 years. Medical surveillance of 6 heterozygous carriers including repeated neck ultrasound examination as well as basal and calcium (pentagastrin)-stimulated calcitonin levels were recommended.

CONCLUSION

Our data emphasize the importance of an interdisciplinary approach to assess the functional and clinical significance of novel RET variants. In the absence of functional studies, the plausibility of the pathologic significance of a detected endocrine genetic variant can be estimated by in silico methods such as computational analysis of protein structure and biophysical differences or comparative database search for evolutionary conservation.