Retinocytoma. A benign variant of retinoblastoma

Six examples of a distinctive benign retinal tumor, occurring in five children and treated only by enucleation, were studied by light and electron microscopy and tested for S-100 protein, a glial-cell tissue marker. The small placoid, noninvasive lesions were composed entirely of benign-appearing cells with numerous fleurettes. These tumors showed no necrosis or mitotic activity. Ultrastructurally, they were composed predominantly of neuronal cells exhibiting photoreceptor differentiation. Some tumor cells had cytologic features of Müller's fibers and other glial cells that in one lesion stained positively for S-100 protein. In two patients there was a family history of retinoblastoma. All children were alive and well at follow-up examinations conducted three to 14 years after enucleation. To expand our concept of retinoblastoma to include this benign variant, we propose the term "retinocytoma." Although clinically and morphologically distinct from retinoblastoma, retinocytoma should carry the same genetic implication as its malignant counterpart.