Retinoblastoma is a cancer of the retina, a light-sensitive layer of tissue in the eye. Among children, it is the most common malignant tumor that starts in eye. Still, it is very rare, with only about 250 to 300 cases diagnosed each year in the United States. It usually occurs before age five, and most of these cases occur in children under two. The disease accounts for 3% of cancers in children.
Twenty-five percent to 40% of retinoblastoma cases are hereditary. In these cases, the patient has a mutation in a tumor suppressor gene known as RB1. This mutation is found in the DNA in every cell of the patient’s body. It is usually inherited from a parent, but it also can be a new mutation that starts with the patient. In both cases, this form of the disease can be passed down to the next generation. This type of retinoblastoma usually develops before age 1.
Sporadic retinoblastoma makes up the other 60% to 75% of cases. It is not inherited or passed down. Instead, a single cell mutates seemingly at random. It then begins dividing and eventually grows into a malignant tumor. This form of the disease usually occurs in children over age 1.
Types of Retinoblastoma
Unilateral retinoblastoma affects one eye and accounts for 60% to 75% of cases. About 85% of these diagnoses are the sporadic form of the disease. The rest are hereditary cases.
Bilateral retinoblastoma affects both eyes. It is almost always hereditary. Patients with bilateral retinoblastoma are typically diagnosed at a younger age (less than one year old) than those with unilateral disease.
PNET (primitive neuroectodermal tumors) retinoblastoma occurs when an associated tumor forms in primitive nerve cells in the brain. This form of the disease occurs only in children with hereditary retinoblastoma. It affects just 5% of patients with bilateral retinoblastoma. It also is known as trilateral retinoblastoma.
Some cases of retinoblastoma can be passed down from one generation to the next. Genetic counseling may be right for you. Learn more about the risk to you and your family on our genetic testing page.