An immunopathologic study of retinoblastoma protein.

We investigated the immunoreactivity of the retinoblastoma protein in eight retinoblastoma tumors of different stages of differentiation. All undifferentiated tumor cells failed to show immunoreactivity. In one patient, who had a family history of retinoblastoma and had been treated by radiation, the tumor had a large area of undifferentiated cells and small independent retinocytomas. The tumor cells in the retinocytoma and the cone cells in the adjacent retina, but not the undifferentiated tumor cells, showed positive staining with two anti-Rb antibodies. The immunoreactivity may be related to radiation or differentiation of retinoblastoma and cone cells.