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.

Automated summary

Medullary thyroid cancer (MTC) is a rare disease that can be sporadic or genetically determined. The significance of RET signaling pathways in the pathogenesis of MTC is suggested by the presence of RET pathogenic variants in aggressive forms of both sporadic and genetically determined MTC. However, the relationship between RET codon-related MTC aggressiveness is still debated, and other factors such as RET polymorphisms, epigenetic factors, environmental factors, MET alterations, and RAS family genetic alterations may also impact the progression of the disease.