Spontaneous and Urethan-Induced Tumor Incidence in B6C3F1 versus B6Cf1 Mice

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Abstract
The incidences of spontaneous tumors of the murine hybrids (C57BL/6J x C3Hf)Fl (B6C3F1) and (C57BL/6J x BALB/c)Fl (B6CF1) were compared in untreated mice kept until 110 weeks of age. Male B6C3F1 and B6CF1 mice had respectively 16 % and 20 % incidence of lymphomas, 26 % and 4 % of liver tumors and 12 % and 22 % of lung tumors. Among B6C3F1 and B6CF1 females, a 36 % and 12 % incidence of lymphomas, a 6 % and zero incidence of liver tumors, and a 4 % and 16 % of lung tumors were observed. A few other tumors were seen in both hybrids. Groups of male and female mice of the 2 hybrids received 5 i.p. injections of 1000 mg/kg urethan once every other day starting at 10 days of age, and were kept under observation until 65–80 weeks of age. Treated B6C3F1 mice had an earlier mortality than B6CF1 mice due to tumor development. The statistical analysis, allowing for survival, showed a significantly higher lymphoma incidence in male and female B6C3F1 than B6CF1 mice, which had instead a higher incidence of lung tumors. Hepatocellular tumors were seen in both sexes of the 2 hybrids, with a higher frequency in B6C3F1 mice. Male mice of both hybrids had a higher incidence of liver tumors than females.