A 10-year-old female rabbit developed an unencapsulated and asymmetrical superficial dermal mass on the neck. The tumour was invasive with central ulceration and contained three different histological components, namely trichoblastomatous, basal cell carcinoma (BCC)-like and undifferentiated carcinomatous. In the trichoblastomatous component, which occupied most of the tumour, epithelial neoplastic cells formed ribbon-like cellular trabeculae with a palisaded appearance and stromal giant cells. The BCC-like component was a unique lesion composed of epithelial foci and sarcomatous stroma. The sarcomatous stroma consisted of pleomorphic mesenchymal cells with collagen fibres and frequent giant cells with one or more bizarre nuclei. In the undifferentiated carcinomatous component, neoplastic cells had a sheet-like growth pattern without trichoblastic or squamous differentiation. Immunohistochemically, neoplastic epithelial cells were positive for p63 and cytokeratin (CK) while the stromal and giant cells were immunopositive for vimentin but negative for CK and p63. This is the first report of a malignant trichoblastoma with a sarcomatous stroma in animals.

immunohistochemistry

malignant trichoblastoma

rabbit

sarcoma

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