Costenbader Memorial Lecture: Genesis and genetics of retinoblastoma.

(1) The incidence of retinoblastoma is 1/20,000. (2) About 94% of all retinoblastoma cases are sporadic, while 6% are familial. (3) The hereditary retinoblastomas, whether sporadic or familial, represent 40% of all cases. (4) A new dominant germinal mutation is responsible for 100% of the bilateral sporadic cases and for 10-15% of the unilateral sporadic cases. (5) Knudson's multistage mutation is the best explanation of retinoblastoma's behaviour. (6) A deletion of the long arm of a D-chromosome (13q14) may be the cause of some, if not of all retinoblastomas. (7) The main difficulty in genetic counseling is the lack of means for identifying which sporadic unilateral retinoblastomas are due to a new germinal mutation.