Immunohistochemical characterisation of a canine case of granular cell type trichoblastoma: A case report

Herein we describe a case of granular cell type trichoblastoma in a dog. A nine-year-old, intact male Scottish terrier presented with a solitary, exophytic and non-ulcerated nodule on the shoulder. Histopathologically, the nodule showed a ribbon-like structure, which was composed of branching cords of epithelial cells surrounded by fibrous stroma. In addition, islands of large clear cells were also noted. The clear cells showed eccentric nuclei and abundant cytoplasmic vacuoles, which were strongly positive for periodic acid-Schiffstaining. Cytoplasmic immunostaining for cytokeratin (CK) 14 and nuclear immunostaining for p63 were observed in the neoplastic cells. In contrast, CK18 staining was scant. Furthermore, the hair bulge stem cell marker CK15 showed strong cytoplasmic staining. Based on these histopathological and immunohistochemical findings, the tumour was diagnosed as a granular cell type trichoblastoma, which is rarely reported in dogs.