Incidence and type of tumors induced in C57BL bg/bg mice and +/bg littermates by oral administration of DMBA.

As an attempt to study the effect of the beige (bg) mutation on chemical carcinogenesis, 65 C57Bl/bg/bg mice and 83 +/bg littermate controls received DMBA in five weekly intragastric doses. The incidence of tumors of different histological types was monitored through observation periods ranging between 165 and 500 days. By 165 days after the first DMBA feeding, 18% of the +/bg and 31% of the bg/bg mice had developed tumors. The beige mice had a higher incidence of epithelial and non-epithelial tumors arising in cutaneous or subcutaneous sites than the controls. The total incidence of lymphomas was similar in the two groups. However, lymphomas appeared somewhat earlier in beige than in control mice. Altogether 33 +/bg and 27 bg/bg mice were followed for 500 days. By this time, 73% of the +/bg and 78% of the bg/bg mice had developed tumors. The beige group showed a higher incidence of non-thymic lymphomas than the controls. In contrast, the incidence of thymic lymphoma, cutaneous epithelial tumors and bile-duct adenomas was similar in the two groups or higher in +/bg that in bg/bg mice. The results suggest that the bg mutation causes a certain defect in a mechanism that may prevent or delay the onset of non-thymic lymphomas and of epithelial and non-epithelial cutaneous tumors in DMBA-treated mice. The differences between the two groups were smaller than those previously reported in relation to the increased susceptibility of beige mice to certain transplanted tumors, attributed to the known defect in natural killer (NK) activity in the beige mice. The reduced differential in the DMBA system may be due to the partial reduction of NK activity, induced by the carcinogen, as reported previously (Ehrlich et al., 1980) and confirmed in the present study.