No correlation between RET immunostaining and the codon 918 mutation in sporadic medullary thyroid carcinoma

Introduction: Medullary thyroid carcinoma (MTC) occurs sporadically or as p art of the inherited cancer syndrome, multiple endocrine neoplasia (MEN) ty pe 2. The MEN2 gene has been identified as the RET proto-oncogene. Mutation s in the RET proto-oncogene are associated with the pathogenesis of MTC. Ap proximately 23-40% of sporadic MTCs (sMTCs) have a somatic RET codon 918 mu tation within the catalytic core of the tyrosine kinase, which is a mutatio n found in over 98% of all MEN 2B cases as a germline mutation. Methods: In or der to elucidate the role of this mutation, we examined 40 sMTCs for th e codon 918 mutation. Simultaneously, we looked for overexpression of the R ET protein by means of immunohistochemistry with a newly developed RET anti body. Results: In 8 of 40 tumors (20%), we were able to find a RET codon 91 8 mutation. Nine of 4o tumors (22.5%) showed immunoreactivity with the RET antibody. Conclusion: The presence of the somatic RET codon 918 mutations d id not correlate with the presence of positive RET immunostaining.