Basal cell adenocarcinoma on bulbar conjunctiva of third eyelid in a dog.

An 8-year-old castrated Toy poodle presented with swelling and proptosis of the right third eyelid caused by an exophytic mass on the bulbar surface. Histologically, the mass was composed of stratified neoplastic basaloid cells, arranged in nests and interconnecting islands, which were mixed with tubular structures. Immunohistochemically, the basaloid cells were positive for p63 and cytokeratin (CK) 14, and the inner epithelial cells of the tubular structures were positive for CK7, CK8, and CK19. According to these findings, the mass was diagnosed as a basal cell adenocarcinoma. Although basal cell adenocarcinoma is rare in animals, it should be included in the list of differential diagnoses for superficial tumors of bulbar conjunctiva of third eyelid in dogs.