Abstract
An excess of cancer deaths was found in grandparents of 308 children with retinoblastoma. This excess was found in all types of retinoblastoma, unilateral and bilateral, sporadic and familial. We postulated that the excess could be the result of a factor of susceptibility to cancer, different from the retinoblastoma gene, which would increase the mutation rate in retinal and germ cells as well as in other tissues.