Craniopharyngioma is a rare tumor occurring in the sellar region comprising 3% of all intracranial tumors. To elucidate the contribution of β-catenin gene mutation to tumorigenesis, we examined genetic alterations and expression of β-catenin in 10 cases of adamantinomatous and 6 cases of papillary craniopharyngiomas. β-Catenin gene mutations were found in all of the adamantinomatous and none of the papillary craniopharyngiomas. Immunohistochemically, all cases of adamantinomatous craniopharyngioma showed cytoplasmic and nuclear expression of β-catenin. In contrast, papillary craniopharyngiomas showed exclusively membranous expression. The results suggest that adamantinomatous- and papillary-type craniopharyngiomas are not only clinicopathologically, but also genetically, distinctive variants. Mutation of the β-catenin gene therefore seems to play an important role in the tumorigenesis of adamantinomatous craniopharyngioma. Among the adamantinomatous-type tumors, β-catenin-positive mesenchymal cells were observed in two cases. Microdissection-based mutational analysis revealed that these mesenchymal cells also harbor the same β-catenin gene mutations as those of epithelial cells, suggesting their tumorous nature. Thus, at least a subset of adamantinomatous craniopharyngioma is considered to be biphasic.
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