The article presents a statistical study of retinoblastoma, a type of eye cancer, and proposes that it is caused by two mutational events. In the dominantly inherited form, one mutation is inherited from a parent, and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells. The second mutation leads to an average of three retinoblastomas per individual with the first mutation. Using Poisson statistics, this number explains the variation in tumor occurrence among carriers, including those with no tumors, unilateral, and bilateral tumors. The study analyzed 48 cases of retinoblastoma and found that approximately 48% of cases are bilateral, suggesting a hereditary origin. The distribution of tumors among carriers is consistent with a Poisson distribution, with a mean of three tumors per carrier. This supports the hypothesis that retinoblastoma is caused by two mutations. The mutation rates for the first and second mutations are estimated to be approximately equal, with the germinal mutation possibly arising from a delayed mutation. The study also discusses the relationship between mutation rates and the incidence of retinoblastoma. The germinal mutation rate is estimated to be about 5 × 10⁻⁶ per generation, while the somatic mutation rate is approximately 2 × 10⁻⁷ per year. These rates are consistent with the hypothesis that retinoblastoma is caused by two mutations. The study also notes that hereditary cases develop earlier and are more likely to have multiple tumors, while nonhereditary cases are typically unifocal. The data support the two-mutation hypothesis, which is consistent with current understanding of cancer mutational origins. The study concludes that retinoblastoma can be caused by two mutations, each occurring at a rate of about 2 × 10⁻⁷ per year. One of these mutations may be inherited, and those who inherit a mutation develop tumors earlier than those with the nonhereditary form. The study also notes that the two-mutation hypothesis is consistent with the two-stage hypothesis of carcinogenesis, where each stage may result from more than one mutation.The article presents a statistical study of retinoblastoma, a type of eye cancer, and proposes that it is caused by two mutational events. In the dominantly inherited form, one mutation is inherited from a parent, and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells. The second mutation leads to an average of three retinoblastomas per individual with the first mutation. Using Poisson statistics, this number explains the variation in tumor occurrence among carriers, including those with no tumors, unilateral, and bilateral tumors. The study analyzed 48 cases of retinoblastoma and found that approximately 48% of cases are bilateral, suggesting a hereditary origin. The distribution of tumors among carriers is consistent with a Poisson distribution, with a mean of three tumors per carrier. This supports the hypothesis that retinoblastoma is caused by two mutations. The mutation rates for the first and second mutations are estimated to be approximately equal, with the germinal mutation possibly arising from a delayed mutation. The study also discusses the relationship between mutation rates and the incidence of retinoblastoma. The germinal mutation rate is estimated to be about 5 × 10⁻⁶ per generation, while the somatic mutation rate is approximately 2 × 10⁻⁷ per year. These rates are consistent with the hypothesis that retinoblastoma is caused by two mutations. The study also notes that hereditary cases develop earlier and are more likely to have multiple tumors, while nonhereditary cases are typically unifocal. The data support the two-mutation hypothesis, which is consistent with current understanding of cancer mutational origins. The study concludes that retinoblastoma can be caused by two mutations, each occurring at a rate of about 2 × 10⁻⁷ per year. One of these mutations may be inherited, and those who inherit a mutation develop tumors earlier than those with the nonhereditary form. The study also notes that the two-mutation hypothesis is consistent with the two-stage hypothesis of carcinogenesis, where each stage may result from more than one mutation.