Investigation of lung tumour induction in C3H/HeH mice, with and without tumour promotion with urethane, following paternal X-irradiation.

In series of papers Nomura has reported that parental irradiation can lead to an enhanced incidence of lung and other tumours. However, in a recent study with BALB/cJ mice, using optimum conditions as defined by Nomura, we were unable to confirm this. We have now repeated the investigation using a different inbred strain, C3H/HeH, with and without tumour promotion in the F1 by urethane, again using protocols defined by Nomura. In a series of replicate studies spanning over 2 years, males were exposed to single, acute doses of 0, 250 and 500 cGy X-rays and thereafter placed with two females each in each of two consecutive weeks. Half the offspring from each treatment group and each week of mating were given 5 mmol/kg body weight of the urethane, while the remainder remained untreated. Most of the offspring produced were killed and scored for lung tumours at 6 months of age, while the rest were examined at 12 months of age. The proportion of fertile females and litter size provided evidence of a dose-dependent mutational response to the paternal irradiation, but no trace of a radiation-enhanced lung tumour incidence was detected among the progeny, whether in the urethane or non-urethane groups at 6 or 12 months of age, and whether assessed by numbers of mice with tumours, clusters of tumours, or cluster size. As seen in the BALB/cJ study, significant differences among different replicates were found, again suggesting a cyclical or seasonal variation in tumour incidence, but the variations seen with the two strains were not the same. The need for concurrent controls for tumour work was, nevertheless, again indicated. The overall findings do not therefore accord with those of Nomura. Furthermore, they do not support the causal association between the raised incidence of childhood leukaemia and non-Hodgkins lymphoma near Sellafield and the father's recorded radiation exposure during employment in the nuclear industry, as suggested by the Gardner report.