Four cases of medullary thyroid carcinomas associated with multiple endocrine neoplasia 2B with rearranged during transfection codon M918T mutation in the same family.

Multiple endocrine neoplasia (MEN) with medullary thyroid carcinoma (MTC) is associated with rearranged during transfection (RET) mutations. The authors encountered four cases of MTC-related MEN type 2B (MEN2B) with RET codon M918T mutation in one family. Case 1 included a 19 year-old male diagnosed with MTC with lung metastases. Genetic testing revealed an RET codon M918T mutation, which indicated MEN2B. The patient responded partially to vandetanib and the disease has shown no progression in 25 months. Case 2 involved the mother of the patient in Case 1. She underwent total thyroidectomy (TT) when diagnosed with MTC-related MEN2B at 12 years of age, but was not counseled adequately. Cases 3 and 4 involved the sisters of the Case 1 patient and were assessed after Case 1 was diagnosed. Genetic testing revealed the same mutation. Case 3 was diagnosed with MTC and underwent TT. Case 4 was asymptomatic but underwent prophylactic TT; histopathologic examination revealed MTC tissue. Prophylactic TT prevented MTC from being detected at an advanced state. Genetic counseling is essential in treating MEN2B. The mother was uninformed about the genetic characteristics of MEN2B, delaying the detection of MTC in her children. The present study reaffirms the importance of family history and screening.