Mechanism of carcinogenesis by germline mutation of protooncogene in hereditary tumors

Germline mutations in one of two alleles of c-ret, c-met and c-kit protooncogenes have been revealed to be the causes of three autosomal dominant hereditary tumors; multiple endocrine neoplasia type 2(MEN2), hereditary papillary renal cell carcinoma (HPRCC), and familial gastrointestinal stromal tumor(FGIST), respectively. Patients with MEN2A have missense mutations at extracellular cysteine rich domain of c-ret, those with MEN2B have missense mutations at tyrosine kinase domain of c-ret, those with HPRCC have missense mutations at tyrosine kinase domain of c-met, and those with FGIST have in-frame deletion mutations at juxtamembrane domain of c-kit. All of these mutations are assumed to cause constitutive activation of protooncogenes without binding to ligands, resulting in tumor formation.