Retinoblastoma does not develop in approximately ten percent of patients who carry the heritable mutation. Hereditary retinoblastomas usually occur at a younger age and are more likely bilateral and multicentric. In addition, the patient has a higher risk of developing tumors in other parts of the body. The average time between presentation with retinoblastoma and the appearance of a second cancer is between 10.4 and 13 years. The most common non-ocular cancer is osteogenic sarcoma, other tumors such as rhabdomyosarcoma, chondrosarcoma, spindle cell sarcoma, neuroblastoma, glioma, leukemia, sebaceous cell carcinoma, squamous cell carcinoma, and malignant melanoma have also been reported.
Genetic counseling is an important aspect in the treatment of retinoblastoma.
The key is identifying patients who carry the heritable mutation, since these patients have an approximately 80 to 90 percent chance of developing retinoblastoma and a 50 percent chance of passing the gene to their future children. Several clinical features help to identify children that may carry the heritable form of retinoblastoma. Patients with bilateral or multifocal retinoblastomas and those with a positive family history of retinoblastoma are assumed to have the heritable retinoblastoma mutation. It is important to remember that the retinoblastoma gene produces cancer in approximately 80 to 90 percent of patients who carry the gene and, therefore, about 40 percent of the patients' offsprings will have retinoblastoma, while some offspring may simply carry the gene and never develop the disease. The aim of genetic screening in families with hereditary retinoblastoma is to identify those persons who carry a mutation and are at risk for tumor development.