Secondary neoplasms after retinoblastoma treatment: retrospective cohort study of 754 patients in Japan.

OBJECTIVE Little is known about the incidence of secondary neoplasms among survivors of retinoblastoma in Japan. The objective of our study was to analyze the cumulative incidence rate of secondary neoplasms following retinoblastoma and to investigate the risk factors of developing secondary neoplasms. METHODS We conducted a retrospective cohort study of 754 retinoblastoma patients who visited the National Cancer Center Hospital in Tokyo between 1964 and 2007. The cumulative incidence rate curves were drawn using the competing risk method and compared with the Gray's test. Using competing risk regression analysis, multivariate analysis estimated the subdistribution hazard ratio of factors related to the development of secondary neoplasms. RESULTS The median length of follow-up was 108 months (0-594 months). Twenty-one (2.8%) patients developed 23 secondary neoplasms in total. The cumulative incidence rates of secondary neoplasms after retinoblastoma treatment were 2.4% at 10 years after diagnosis, 4.3% at 20 years, 6.4% at 30 years and 19.1% at 40 years. Ten patients (1.3%) died and 723 (95.9%) were alive without developing secondary neoplasms. The subdistribution hazard ratios of hereditary retinoblastoma and external beam irradiation were 4.85 (95% confidence interval = 0.74-31.85) and 4.76 (95% confidence interval = 0.69-33.09), respectively. CONCLUSIONS We demonstrated the cumulative incidence rate of secondary neoplasms following retinoblastoma in Japan. The subdistribution hazards ratios of hereditary retinoblastoma and external beam irradiation were high but not significant because of statistical power. The long-term follow-up of retinoblastoma survivors is warranted to understand secondary neoplasm risk.