S-antigen immunoreactivity in trilateral retinoblastoma.

Using monoclonal antibody MAbA9-C6, which identifies an antigenic determinant of S-antigen retained in fixed tissue sections, we investigated S-antigen immunoreactivity in the ocular and brain tumors of four cases of trilateral retinoblastoma. In the eye, S-antigen immunoreactivity was present in all retinoblastomas examined, as well as one retinocytoma characterized by benign appearing cells including fleurettes. S-antigen immunoreactivity was focally present in two of the four brain tumors examined. Additionally, two intraocular medulloepitheliomas, one of which contained well-defined rosettes, and 16 primary intracranial tumors, including seven pineal gland tumors and nine other lesions, some of which histopathologically may resemble retinoblastoma, were examined. S-antigen immunoreactivity was observed in two pineal gland tumors but not the remaining nine primary intracranial neoplasms or the two intraocular medulloepitheliomas. Our results further substantiate the immunologic relationship between the retina and the pineal gland, and tumors originating in these tissues.