RET and medullary thyroid gland carcinoma: RET downstream pathways (e.g., RAS/RAF/MAPK and PI3K/AKT/mTOR), other intracellular pathways (e.g., NOTCH), other main intracellular mechanisms (e.g., proteasome), other cell membrane receptors (e.g., somatostatin receptors – SSTRs) and immune response regulation, could influence MTC oncogenesis and could be a potential target of specific treatments.