Risk of new cancers after radiotherapy in long-term survivors of retinoblastoma: an extended follow-up.
PURPOSE: Many children diagnosed with retinoblastoma (Rb) survive into adulthood and are prone to subsequent cancers, particularly hereditary patients, who have germline Rb-1 mutations. We have extended the follow-up of a large cohort of Rb patients for 7 more years to provide new information on the risk of additional cancers after radiotherapy in long-term survivors. PATIENTS AND METHODS: We analyzed the risk of new cancers through 2000 in 1,601 Rb survivors, diagnosed from 1914 to 1984, at two US medical centers. The standardized incidence ratio (SIR) was calculated as the ratio of the observed number of cancers after hereditary and nonhereditary Rb to the expected number from the Connecticut Tumor Registry. The cumulative incidence of a new cancer after hereditary and nonhereditary Rb and radiotherapy was calculated with adjustment for competing risk of death. RESULTS: Subsequent cancer risk in 963 hereditary patients (SIR, 19; 95% CI, 16 to 21) exceeded the risk in 638 nonhereditary Rb patients (SIR, 1.2; 95% CI, 0.7 to 2.0). Radiation further increased the risk of another cancer in hereditary patients by 3.1-fold (95% CI, 2.0 to 5.3). Hereditary patients continued to be at significantly increased risk for sarcomas, melanoma, and cancers of the brain and nasal cavities. The cumulative incidence for developing a new cancer at 50 years after diagnosis of Rb was 36% (95% CI, 31% to 41%) for hereditary and 5.7% (95% CI, 2.4% to 11%) for nonhereditary patients. CONCLUSION: Hereditary Rb predisposes to a variety of new cancers over time, with radiotherapy further enhancing the risk of tumors arising in the radiation field.