Anti-CTNNB1 monoclonal antibody, clone 0G3

Pilomatrixoma, an uncommon, usually benign cutaneous appendageal tumor, shows differentiation toward the hair follicle matrix cell. It undergoes various histopathologic stages, early on displaying epithelial and shadow cells along with granulomatous inflammation. In later stages, illustrated by this unusual case, epithelial cells disappear and are replaced by calcification and ossification. Immunohistochemistry in the current case showed transitional cell reactivity for beta-catenin, probably linking the tumor to a mutation in the beta-catenin gene CTNNB1. There was also transitional cell positivity for cyclin D1, a marker found in matrical cells of the human hair follicle. While pilomatrixoma occurs occasionally in the eyelid, the ossified eyelid variant in the current case is very rare, with only one preceding description in the literature.

We describe a case of papillary thyroid carcinoma with fibromatosis/fasciitis-like stroma (PTC-FLS) that contained the rare BRAF c.1799_1801delTGA (p.V600_K601delinsE) mutation, which has not previously been reported in this tumour, as well as the CTNNB1 c.133T>C (p.S45P) mutation. We also report the novel observation that spindle cells of the mesenchymal component exhibit diffuse nuclear but not cytoplasmic expression of SOX11, whereas the malignant epithelial cells did not. This suggests that immunoreactivity for SOX11 can be an alternative diagnostic tool for evaluating cases of PTC-FLS where the nuclear expression of beta-catenin is ambiguous.