Background: A small number of children with unilateral retinoblastoma later develop retinoblastoma in the contralateral eye (metachronous bilateral retinoblastoma).
Methods: We analysed the clinical and genetic characteristics of children with sporadic unilateral retinoblastoma to identify risk factors for the development of metachronous bilateral disease.
Results: Fifteen (3.1%) of 480 children with unilateral retinoblastoma later developed metachronous bilateral retinoblastoma (latency period >30 days). The maximum latency period was 2.3 years after initial diagnosis. Nine (22.5%) of 40 children with a RB1 mutation detectable in blood developed metachronous bilateral disease while all 155 children proved to be without a germline RB1 mutation remained unilaterally affected. Clinically, the risk of developing metachronous bilateral retinoblastoma was higher for age at diagnosis ≤0.5 years compared with >0.5 years (19.6% vs 1.2%), and for multifocal compared with unifocal unilateral retinoblastoma (17.1% vs 2.2%).
Conclusions: This study shows that an oncogenic RB1 mutation in the blood is a risk factor for metachronous bilateral retinoblastoma. Additional clinical risk factors for metachronous bilateral disease are diagnosis at young age (≤0.5 years) and multifocal unilateral retinoblastoma. Early genetic analysis may identify children at high risk of developing metachronous bilateral disease and may help to preserve vision using risk-adapted follow-up and early treatment.