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.