INTRODUCTION
Multiple endocrine neoplasia type 2 (MEN2) is an
autosomal-dominant hereditary cancer syndrome caused
by missense mutations in the RET (REarranged during
Transfection) proto-oncogene, and these result in the gainof-
function of the encoding receptor tyrosine kinase (1). The
estimated prevalence is 2.5 per 100,000 in the general
population. MEN2 shows a high penetrance for medullary
thyroid carcinoma (MTC), which is a rare calcitonin (Ct)-
secreting tumor derived from thyroid parafollicular or Ccells
of the thyroid; these cells are themselves derived from
the neural crest. Most patients with MTC have the sporadic
(i.e., non-familial) form of the tumor, while 25–30% present
with the hereditary form. MEN2 syndrome occurs in three
clinically distinct varieties with variable penetrance of MTC,
pheochromocytoma, and hyperparathyroidism. Early identification
of patients with MTC changes the presentation
from a clinically evident tumor to a preclinical disease,
resulting in a higher cure rate of the affected patients with
much better prognoses (2). Each variant of MEN2 results
from a different mutation of the RET gene with good
genotype-phenotype correlations