Common mutations of β-catenin in adamantinomatous craniopharyngiomas but not in other tumours originating from the sellar region

Dysregulation of the Wnt signalling pathway contributes to developmental abnormalities and carcinogenesis of solid tumours. Here, we examined beta-catenin and adenomatous polyposis coli (APC) by mutational analysis in pituitary adenomas (n=60) and a large series of craniopharyngiomas (n=41). Furthermore, the expression pattern of beta-catenin was immunohistochemically analysed in a cohort of tumours and cysts of the sellar region including pituitary adenomas (n=58), craniopharyngiomas (n=57), arachnoidal cysts (n=8), Rathke's cleft cysts (n=10) and xanthogranulomas (n=6). Whereas APC mutations were not detectable in any tumour entity, beta-catenin mutations were present in 77% of craniopharyngiomas, exclusively of the adamantinomatous subtype. All mutations affected exon 3, which encodes the degradation targeting box of beta-catenin compatible with an accumulation of nuclear beta-catenin protein. In addition, a novel 81-bp deletion of this exonic region was detected in one case. Immunohistochemical analysis confirmed a shift from membrane-bound to nuclear accumulation of beta-catenin in 94% of the adamantinomatous tumours. Aberrant distribution patterns of beta-catenin were never observed in the other tumour entities under study. We conclude that beta-catenin mutations and/or nuclear accumulation serve as diagnostic hallmarks of the adamantinomatous variant, setting it apart from the papillary variant of craniopharyngioma.