The management of retinoblastoma

Based upon observations on 48 cases of retinoblastoma and published reports, the hypothesis is developed that retinoblastoma is a cancer caused by two mutational events. In the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells. The second mutation produces an average of three retinoblastomas per individual inheriting the first mutation. Using Poisson statistics, one can calculate that this number (three) can explain the occasional gene carrier who gets no tumor, those who develop only unilateral tumors, and those who develop bilateral tumors, as well as explaining instances of multiple tumors in one eye. This value for the mean number of tumors occurring in genetic carriers may be used to estimate the mutation rate for each mutation. The germinal and somatic rates for the first, and the somatic rate for the second, mutation, are approximately equal. The germinal mutation may arise in some instances from a delayed mutation.

Anesthetic drugs administered to immature animals may cause neurohistopathologic changes and alterations in behavior. The authors studied association between anesthetic exposure before age 4 yr and the development of reading, written language, and math learning disabilities (LD). This was a population-based, retrospective birth cohort study. The educational and medical records of all children born to mothers residing in five townships of Olmsted County, Minnesota, from 1976 to 1982 and who remained in the community at 5 yr of age were reviewed to identify children with LD. Cox proportional hazards regression was used to calculate hazard ratios for anesthetic exposure as a predictor of LD, adjusting for gestational age at birth, sex, and birth weight. Of the 5,357 children in this cohort, 593 received general anesthesia before age 4 yr. Compared with those not receiving anesthesia (n = 4,764), a single exposure to anesthesia (n = 449) was not associated with an increased risk of LD (hazard ratio = 1.0; 95% confidence interval, 0.79-1.27). However, children receiving two anesthetics (n = 100) or three or more anesthetics (n = 44) were at increased risk for LD (hazard ratio = 1.59; 95% confidence interval, 1.06-2.37, and hazard ratio = 2.60; 95% confidence interval, 1.60-4.24, respectively). The risk for LD increased with longer cumulative duration of anesthesia exposure (expressed as a continuous variable) (P = 0.016). Exposure to anesthesia was a significant risk factor for the later development of LD in children receiving multiple, but not single anesthetics. These data cannot reveal whether anesthesia itself may contribute to LD or whether the need for anesthesia is a marker for other unidentified factors that contribute to LD.