Intraocular carcinosarcoma with osteosarcomatous component arising from iridociliary adenocarcinoma in a dog.

A 9-year-old neutered male Labrador Retriever presented with increased intraocular pressure in the left eye and underwent enucleation for a suspected intraocular tumor. Grossly, a white to greyish-white solid mass occupied the anterior segment and was partially contiguous with the lens. Histologically, the tumor exhibited biphasic proliferation of epithelial and mesenchymal components. The mesenchymal component showed osteoid formation, and transitional features were observed between the two components. Based on histological and immunohistochemical findings, the tumor was diagnosed as a carcinosarcoma composed of an iridociliary adenocarcinoma component and an osteosarcomatous component. This is the first report of carcinosarcoma in the canine eye, expanding the understanding of the morphological diversity and histogenetic characteristics of canine iridociliary tumors.