Differentiated basal cell carcinoma in a Cape clawless otter (Aonyx capensis).

Basal cell carcinoma with folliculoapocrine differentiation was diagnosed in a male Cape clawless otter (Aonyx capensis) aged >8 years. A tumour mass in the left submandibular region was removed surgically, but another tumour subsequently appeared on the left cheek. In addition, necropsy revealed a subcutaneous tumour mass at the excision site. Histologically, the tumours consisted of lobules or islands of basaloid cells, frequently with central keratinization and tubular structures. The presence of isthmic keratinization and apocrine differentiation was confirmed by immunolabelling for cytokeratins, and a few cytokeratin-positive tumour cells were found in a submandibular lymph node. The neoplasm, characterized by its metachronous and recurrent nature, metastasis to the local lymph node and amyloidosis, closely resembled human differentiated basal cell carcinoma, both clinically and pathologically.