Second primary tumours in hereditary- and nonhereditary retinoblastoma patients treated with megavoltage external beam irradiation.

The purpose of this retrospective study is to investigate the influence of 45 Gy megavoltage external beam radiotherapy on the occurrence of second primary tumours in hereditary- and non-hereditary retinoblastoma patients. Eighty-seven hereditary and 19 non-hereditary patients were irradiated for retinoblastoma. The follow-up of the hereditary patients ranged from 4-23 years (mean 12.4 years), of the non-hereditary patients from 6-23 years (mean 12 years). In the hereditary group 4 patients developed a second primary tumour (2 rhabdomyosarcoma, 1 osteosarcoma, 1 malignant histiocytoma), and 5 patients developed a pineoblastoma. Three second primary tumours were situated inside the radiation field. The latency period ranged from 1.5 to 18 years (mean 4.8 years). None of the non-hereditary patients developed a second primary tumour. The actuarially calculated probability of being free from second primary tumours was 96.9% at 10 years and 89.4% at 20 years (pineoblastoma excluded). The survival was 91.2% at 10 years and 84.2% at 20 years (pineoblastoma excluded). From this study it is suggested that external beam irradiation has a potentiating effect in patients, with the genetic predispopsition for retinoblastoma and who are more susceptible to second primary malignancies.