Identification and significance of multinucleate tumor cells in retinoblastoma.

Multinucleate tumor cells were observed in a case of a retinal tumor suspected to be a retinoma (retinocytoma). On electron microscopy, these cells had characteristics of retinoblastoma. Similar cells were observed in an irradiated model of retinoblastoma grown in a nude mouse. We suggest that the presence of these cells indicates differentiation and/or regression of the tumor.