Retinoblastoma is a rare childhood cancer of the eye. It appears in infants or young children at a frequency of about one in every 15,000 births. In somecases, there is a family (familial) history of the disease. It is curable ifdetected early, but often requires surgical removal of the eye.
The genetic cause of retinoblastoma has been extensively studied. Normally, individuals have two good copies of the retinoblastoma gene (RB-1) on chromosome 13. This RB-1 gene carries the information for making a protein called pRBwhich regulates cell division. When pRB is absent or defective due to defective (mutated) copies of the gene, uncontrolled cell division occurs, and cancer results. These patients also have increased risk of developing other typesof cancer because pRB appears to be involved in many types of cancer besidesretinoblastoma.
Retinoblastoma develops in individuals in whom mutation (an abnormality) hasoccurred in both copies of RB-1. Retinoblastoma is described as a "two-hit" process. It appears that about 40% of patients are born with a defective copyon one gene (first "hit"), inherited from one parent. The second copy is rendered defective by a separate mutation (second "hit") that occurs in the eye.Individuals with an inherited RB-1 defect have a high likelihood of developing retinoblastoma in both eyes. For individuals who do, diagnosis occurs at about age one.
The other 60% of patients inherit two normal copies of RB-1 and develop the disease only after each copy experiences an independent mutation. The likelihood of two independent "hits" is lower, and these individuals are less likelyto develop retinoblastoma in both eyes. For these individuals, average age ofdiagnosis is 2.1 years.
Individuals with familial tumors in only one eye have a high incidence (70%)of recurrence in the other eye, and some patients experience secondary tumorsin other non-ocular tissues of the body. Although chances of developing retinoblastoma decline sharply after age five, for those individuals who have hadretinoblastoma in one eye, there is some possibility of the disease appearing in the other eye at any age into adulthood.
In cases with a family history of retinoblastoma, the child inherits a defective chromosome 13 from one parent. The tumor arises, however, only after a second, spontaneous mutation occurs in one of the cells of the retina; therefore, a situation then exists in which both copies of chromosome 13 carry defective genes. In the majority of cases, however, spontaneous mutations appear tooccur in both copies of chromosome 13.
During diagnosis for retinoblastoma, a white reflection in the pupil of the eye is often the first sign of the disease. The presence of a tumor can be confirmed by an ophthalmologist directly examining the retina through the pupil.
Treatment depends upon the size and number of tumor locations in the eye, aswell as whether the disease is found in one or both eyes. When only one eye is involved, the eye is surgically removed. If both eyes are involved, one eyecan sometimes be saved by treating the tumor with radiation therapy, photocoagulation (use of intense laser light to destroy cancer cells), or cryotherapy (use of intense cold to kill cancer cells). Chemotherapy is increasingly used as a follow-up to one of these treatments. However, some forms of radiation therapy have been shown to promote other cancers, especially of the bone.
Because many patients have a strong predisposition to this disease, frequenteye examinations are recommended, especially after successful treatment for retinoblastoma in order to get the earliest possible warning if the disease recurs. Close monitoring is also important.
In a small percentage of cases, retinoblastoma is fatal because it has already spread through the optic nerve to the brain. However, if diagnosis occurs early, when the tumor is restricted to the eye, 90% of patients can be cured.
No preventative measures are possible for a genetic condition such as retinoblastoma. When expectant parents--or couples who wish to become pregnant--arerelated to anyone who has had retinoblastoma, they should receive genetic counseling. Genetic testing may be recommended to see if a defective gene has been inherited.