Cancer in relatives of retinoblastoma patients.

Medical histories with emphasis on malignant disease were obtained on 1,269 first and second degree relatives of 93 probands with retinoblastoma and on 671 first and second degree relatives of 50 age-matched control children. The number of nonocular malignancies expected to occur in first and second degree relatives of the probands were calculated using the observed number of neoplasms in control families as the standard. Using a Poisson distribution to evaluate the findings, a statistically significant excess of cancer was found in relatives of the probands with retinoblastoma. Gastrointestinal malignancies were particularly common in this population.