Retinoblastoma is a malignant tumor (cancer) of the retina (part of the eye) that generally affects children under the age of 6.
Retinoblastoma occurs when a cell of the growing retina develops a mutation in the RB gene (a tumor-suppressor gene). This mutation causes the cell to grow out of control and become cancerous.
Sometimes this mutation develops in a child whose family has never had eye cancer, but other times the mutation is present in several family members. If the mutation runs in the family, there is a 50% chance that an affected person's children will also have the mutation. They will therefor have a high risk of developing retinoblastoma themselves.
One or both eyes may be affected. A visible whiteness in the pupil may be present. Blindness can occur in the affected eye, and the eyes may appear crossed. The tumor can spread to the eye socket, and to the brain, through the optic nerve. This is a rare tumor, except in families that carry the RB gene mutation.