Childhood Cancers: Retinoblastoma

Retinoblastoma is the most common childhood malignant tumor of the retina, the membrane at the back of the eyeball. About 300 children in the United States develop this cancer each year. The vast majority of retinoblastoma cases occur in very young children: 66 percent occurring before age two and 95 percent before age five. In some instances, retinoblastoma is diagnosed at birth. The tumor may occur in one eye (75 percent) or both eyes (25 percent).

How It Spreads The tumor may be confined to the retina or extend directly to other parts of the eye (commonly the optic nerve). In its later stages, it may spread to the central nervous system or other parts of the body.

What Causes It There are hereditary (40 percent) and nonhereditary (60 percent) forms of retinoblastoma. The hereditary form may be unilateral (one eye) but more typically is bilateral (both eyes). When there is disease in both eyes, it is almost always the hereditary form. There is no racial or gender predilection. The retinoblastoma (RB) gene has been identified on chromosome 13. Retinoblastoma is the best example of a genetic predisposition to cancer. Children who inherit defects in the RB gene have a 90 percent chance of developing retinoblastoma. The incidence of retinoblastoma is increasing because survivors of childhood retinoblastoma are now of an age to have their own children. Families of children with retinoblastoma should have genetic counseling.

Diagnosis

Most children in the United States are diagnosed while the tumor remains within the eye. The tumor is detected by shining a light into the child’s eye and looking for what is called a cat’s eye—a white spot in place of the dark pupil. There may also be symptoms such as poor vision and strabismus (squinting).

It is important for children with retinoblastoma to be seen in a specialized center where physicians have experience in evaluating the size of the tumor and the extent of the disease.

Staging

Several staging systems are used, but for purposes of treatment, retinoblastoma is divided into intraocular (within the eye) and extraocular (spread beyond the eye) disease.

Treatment Overview

Standard Treatment In some cases, it may be possible to destroy the tumor within the eye by using light (laser) treatment (photocoagulation), freezing (cryotherapy), or heat treatment (thermotherapy). Other options include enucleation (removal of the diseased eye), with eventual replacement with an artificial eye, and radiation therapy (brachytherapy or external-beam).

Which of these procedures is used depends on the size of the tumor and whether the child has potentially useful vision.

The use of chemotherapy requires additional investigation, although tumors generally respond in a satisfactory manner to a number of chemotherapy drugs.

Five-Year Survival Over 90 percent if disease is confined to the eye; less than 10 percent if it has spread beyond the eye

Treatment Follow-Up

Children with retinoblastoma, especially the hereditary form, have an increased risk for developing other malignancies later in life and so should be followed closely. Up to 8 percent, for example, may develop bone tumors after eighteen years, and the percentage may be higher with longer follow-up. Second cancers may develop spontaneously or be the result of treatment.