Low frequency of β-catenin gene mutations in pilomatricoma

We investigated β-catenin and adenomatous polyposis coli (APC) gene abnormalities in human pilomatricoma, in which a high incidence of β-catenin gene mutations has been reported. Nucleated tumour cells were microdissected from 20 paraffin-embedded pilomatricomas. Exon 3 of the β-catenin gene was amplified using polymerase chain reaction and sequencing analysis was performed. Immunostaining for β-catenin and lymphoid-enhancer factor-1 was performed using the avidin-biotin-peroxidase method. Dinucleotide repeat markers D5S409 and D5S299 were used for polymerase chain reaction-based microsatellite analysis of the APC gene. The mutation cluster region of the APC gene was amplified using polymerase chain reaction and sequenced. Sequencing analysis revealed β-catenin gene mutations in 30%. All studied samples showed nuclear lymphoid-enhancer factor-1 and cytoplasmic/nuclear β-catenin expression. Loss of heterozygosity was observed in the APC gene, but no mutations in the mutation cluster region were found in seven tumours without β-catenin mutations. The frequency of β-catenin gene mutations was remarkably low, thus suggesting (i) the presence of mutations in other than exon 3 of the β-catenin gene, (ii) a possible role of APC gene abnormalities, or (iii) involvement of other components of the Wingless-type MMTV integration site family pathway.