Variation of second cancer risk by family history of retinoblastoma among long-term survivors.

PURPOSE: To evaluate the risk of second cancer (SC) in long-term survivors of retinoblastoma (Rb) according to classification of germline mutation, based on family history of Rb and laterality. PATIENTS AND METHODS: We assembled a cohort of 1,852 1-year survivors of Rb (bilateral, n = 1,036; unilateral, n = 816). SCs were ascertained by medical records and self-reports and confirmed by pathology reports. Classification of RB1 germline mutation, inherited or de novo, was inferred by laterality of Rb and positive family history of Rb. Standardized incidence ratios and cumulative incidence for all SCs combined and for soft tissue sarcomas, bone cancers, and melanoma were calculated. The influence of host- and therapy-related risk factors for SC was assessed by Poisson regression for bilateral survivors.
RESULTS: We observed a relative risk (RR) of 1.37 (95% CI, 1.00 to 1.86) for SCs in bilateral survivors associated with a family history of Rb, adjusted for treatment, age, and length of follow-up. The risk for melanoma was significantly elevated for survivors with a family history of Rb (RR, 3.08; 95% CI, 1.23 to 7.16), but risks for bone or soft tissue sarcomas were not elevated. The cumulative incidence of SCs 50 years after diagnosis of bilateral Rb, with adjustment for competing risk of death, was significantly higher for survivors with a family history (47%; 95% CI, 35% to 59%) than survivors without a family history (38%; 95% CI, 32% to 44%; P = .004).
CONCLUSION: Rb survivors with bilateral disease and an inherited germline mutation are at slightly higher risk of an SC compared with those with a de novo germline mutation, in particular melanoma, perhaps because of shared genetic alterations.