Ameloblastoma (AB), which is the most common odontogenic tumor, may originate 
from the dental lamina remnants. The expression of CD56, which is a 
transmembrane molecule, is associated with neuroectodermal differentiation of 
the embryonal cells. The aim of this study was to evaluate the expression of 
CD56 in AB, in comparison with other odontogenic cysts. We used formalin-fixed, 
paraffi n-embedded specimens from 34 cases of AB, 10 cases of keratocystic 
odontogenic tumor (KCOT), and 7 cases of dentigerous cyst (DC). We 
immunohistochemically examined CD56, NeuroD1, and N-cadherin expression in these 
tumors as compared with the expression patterns of various epithelial markers. 
Seventy-four percent of AB showed immunopositivity for CD56, and both CD56 and 
N-cadherin were diffusely positive in the outer columnar cells of AB. The 
immunopositivities for NeuroD1 and N-cadherin were also observed in the outer 
cells of AB. None of the DC cases was positive for CD56, whereas half the cases 
of KCOT were positive. Because CD56 is expressed in the inner enamel epithelium 
of enamel organs, the outer columnar cells of AB are likely to be the 
differentiation phenotype of the inner enamel epithelium, which is associated 
with neuroectodermal differentiation. The aberrant NeuroD1 expression may induce 
CD56 expression in AB and KCOT.