Beta-catenin expression in benign and malignant pilomatrix neoplasms

Beta-catenin is a 92-kDa protein, initially identified as a coprecipitating species with the E-cadherin cell-cell adhesive complex. It plays a role in signal transduction in the Wnt signalling pathway and has been identified as an oncogene in colon cancer and melanoma. Exon 3 beta-catenin-activating mutations were found in 75% of cases of pilomatricoma (PM). Previous studies have shown that nuclear and/or cytoplasmic staining may correlate with beta-catenin gene mutation.

Because the immunohistochemical expression of beta-catenin in the nucleus or the cytoplasm correlates with beta-catenin mutation, we studied the immunohistochemical profile of beta-catenin expression in normal scalp hair follicles and in PM and pilomatrix carcinoma (PC).

We reviewed 21 cases of PM and five cases of PC using immunohistochemical staining with commercially available antibody in a standard fashion on formalin-fixed paraffin-embedded tissue samples.

All 26 tumours displayed both nuclear and cytoplasmic staining in the basaloid cells with focal membranous staining. Shadow cells were negative in all tumours. Normal control sections from the scalp displayed nuclear reactivity of the matrical cells, mostly concentrated in the supramatrical zone of hair follicles. Membranous staining was present along the intercellular junctions of the epidermis and along the outer and inner root sheaths of hair follicles. We have found similar patterns of beta-catenin nuclear and cytoplasmic expression in both PM and PC.

Despite the shared beta-catenin expression, the biological behaviour of PM and PC is markedly different. These two tumours probably share the activation of a common cellular pathway that could be related to their shared method of keratinization or a shared dysfunction of the cellular adhesion complex and consequently tumorigenesis. To the best of our knowledge, this is the first report on the beta-catenin immunohistochemical expression profile in PC.