Multiplicity of spontaneous lung tumors in CD-1 mice

The multiplicity of the spontaneous lung tumor in CD-1 mice was investigated in 413 males from 6 different control groups of 2-year carcinogenicity studies with agrochemicals. Among a total of 152 lung tumor bearers, 95 (62.5%) were seen with 1 nodule, 36 (23.7%) with 2 nodules, and 14 (9.2%) with 3 nodules. Three males bore 4 nodules and each of 5, 7, 9 and 10 nodules was seen in one male, respectively. In one control group 20 out of 30 lung tumor bearers had 2 or more nodules presenting a significant heterogeneity among the control groups in terms of the multiplicity of lung tumor nodule.