Definition of Retinoblastoma Retinoblastoma: A malignant eye
tumor usually seen in children, that arises in cells in the
developing retina that contain cancer-predisposing mutations in
both copies of the gene RB1. Abbreviated RB. The most common
sign of RB is a white pupillary reflex to light (leukocoria).
There are two forms of RB: hereditary and sporadic. The
inherited form of RB is usually present at birth as multiple
tumors in both eyes. It is due to the transmission of an RB1
germline mutation followed by an acquired somatic RB1 mutation.
The sporadic form of retinoblastoma has later onset and
typically leads to a single tumor in only one eye. It is due to
acquired mutations in both RB1 genes. Patients with hereditary
RB are at increased risk of developing tumors outside the eye,
including pinealomas (in the pineal gland of the brain),
osteosarcomas, soft tissue sarcomas, and melanomas. When RB is
detected at an early stage, it can sometimes be treated locally
but often requires removal of the eye (enucl