Primary primitive neuroectodermal tumors of the retina and ciliary body in dogs.

We describe the clinical, histological, and immunohistochemical features of primary intraocular primitive neuroectodermal tumors in eight dogs. Four of eight tumors exhibited histological features similar to human retinoblastomas characterized by Flexner-Wintersteiner rosettes, and fleurettes, and demonstrated variable immunoreactivity for retinal markers opsin, S-antigen (S-Ag) and interphotoreceptor retinoid-binding protein (IRBP). All dogs with tumors displaying histological and immunohistochemical features of retinal differentiation were ≤2 years of age.