Lymph node metastasis in hereditary medullary thyroid cancer is independent of the underlying RET germline mutation

Updates on the genetics of multiple endocrine neoplasia

Multiple endocrine neoplasia (MEN) is a group of syndromes with a genetic predisposition to the appearance of endocrine tumors, and shows autosomal dominant transmission. The advent of molecular genetics has led to improvements in the management of MEN in terms of diagnosis, prognosis and therapy. The genetics of MEN is the subject of regular updates, which will be presented throughout this paper. MEN1, the first to be described, is associated with the MEN1 gene. MEN1 is well known in terms of the observed phenotype, with genetic analysis being conclusive in 90% of patients with a typical phenotype, but is negative in around 10% of families with MEN1. Improvement in analysis techniques and the identification of other genes responsable for phenocopies allows the resolution of some, but not all, cases, notably non-familial forms suspected to be fortuitous assocations with tumors. MEN4 is a rare phenocopy of MEN1 linked to constitutional mutations in the CDKN1B gene. Though it closely resembles the phenotype of MEN1, published data suggests the appearance of tumors is later and less frequent in MEN4. MEN2, which results from mutations in the RET oncogene, shows a strong genotype-phenotype correlation. This correlation is particularly evident in the major manifestation of MEN2, medullary thyroid carcinoma (MTC), in which disease aggressiveness is dependent on the pathogenic variant of RET. However, recent studies cast doubt on this correlation between MTC and pathogenic variant. Lastly, the recent description of families carrying a mutation in MAX, which is known to predispose to the development of pheochromocytoma and paraganglioma, and presents a phenotypic spectrum that evokes MEN, suggests the existence of another syndrome, MEN5.

Molecular Basis and Natural History of Medullary Thyroid Cancer: It is (Almost) All in the RET

Medullary thyroid cancer (MTC) is a rare disease, which can be either sporadic (roughly 75% of cases) or genetically determined (multiple endocrine neoplasia type 2, due to REarranged during Transfection RET germline mutations, 25% of cases). Interestingly, RET pathogenic variants (mainly M918T) have also been reported in aggressive forms of sporadic MTC, suggesting the importance of RET signalling pathways in the pathogenesis of MTC. The initial theory of RET codon-related MTC aggressiveness has been recently questioned by studies suggesting that this would only define the age at disease onset rather than the aggressiveness of MTC. Other factors might however impact the natural history of the disease, such as RET polymorphisms, epigenetic factors, environmental factors, MET (mesenchymal-epithelial transition) alterations, or even other genetic alterations such as RAS family (HRAS, KRAS, NRAS) genetic alterations. This review will detail the molecular bases of MTC, focusing on RET pathways, and the potential mechanisms that explain the phenotypic intra- and interfamilial heterogeneity.

Exceptionality of Distant Metastasis in Node-Negative Hereditary and Sporadic Medullary Thyroid Cancer: Lessons Learned

CONTEXT

Risk factors of lymph node and distant metastases have rarely been analyzed in hereditary and sporadic medullary thyroid cancer (MTC) using large genetic-clinical data sets.

OBJECTIVE

This comprehensive investigation aimed to explore risk factors of lymph node and distant metastases and interdependencies between age at thyroidectomy, primary tumor size, lymph node metastasis, and distant metastasis in patients with hereditary and sporadic MTC.

METHODS

We performed comparative analyses of risk factors of metastasis, stratified by hereditary MTC (4 mutational risk categories) and sporadic MTC.

RESULTS

There were 1115 patients with hereditary MTC (307 patients) or sporadic MTC (808 patients). Age at thyroidectomy increased proportionately from 12.2, 22.7, 34.3, and 49.8 years for patients with decreasing mutational risk, compared with 52.1 years for patients with sporadic MTC. Metastatic primary tumors overall were 10.7 to 19.4 mm larger in node-positive patients and 15.9 to 19.3 mm larger in distant metastatic patients at thyroidectomy than nonmetastatic tumors. Distant metastases were noted in 13% to 50% of node-positive vs 0% of node-negative hereditary MTC, and in 23.5% of node-positive vs 1.7% of node-negative sporadic MTC. In multivariable logistic regression analysis for sporadic MTC, lymph node metastasis contributed to distant metastasis (odds ratio 12.4) more than primary tumor size (odds ratios of 7.8, 5.5, and 2.4 for tumors measuring >60, 41-60, and 21-40 mm, respectively).

CONCLUSION

When thyroidectomy is performed before lymph node metastases have developed, distant metastases are exceptional, both in patients with hereditary MTC (irrespective of mutational risk level) and patients with sporadic MTC.

Medullary thyroid carcinoma: recent advances in identification, treatment, and prognosis

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor that represents <5% of all thyroid malignancies and is generally more aggressive than differentiated thyroid cancer. The aim of this study is to provide an update, through review of clinical studies of patients with MTC published between January 1, 2016, and June 1, 2021, on recent advances in the diagnosis and treatment of MTC. This review focuses on updates in biochemical testing, imaging, hereditary disease, surgical management, adjuvant therapies, and prognosis. Recent advances reviewed herein have sought to diagnose MTC at earlier stages of disease, predict when patients with a hereditary syndrome may develop MTC, use functional imaging to assess for distant metastases, perform optimal initial surgery with appropriate lymphadenectomy, employ targeted systemic therapies for patients with progressive metastatic disease, and better predict patient-specific outcomes.