Immunohistochemical demonstration of glial markers in retinoblastomas.

Twenty retinoblastomas were studied immunohistochemically in order to visualize glial cells. In the retina, the glial cells in the ganglion cell layer and the Müller cells were GFAP positive, while only the glial cells of the ganglion cell layer expressed S-100 reactivity. In the tumours S-100/GFAP positive glial cells were found in areas near the retina and along many tumour vessels. Some S-100 reactive cells previously interpreted as tumour cells were refound in a few tumours. In areas with Flexner-Winterstein rosettes and in areas with light cells showing photoreceptor-like differentiation, glial cells reactive for both S-100 and GFAP were demonstrated. The latter findings may represent differentiation in a glial direction in the more mature parts of retinoblastoma.