Table 1. Tumor incidence rate in transgenic mice after N-methyl-N-nitrosourea treatment.

Genotype	Squamous cell carcinoma/papilloma (Stomach)	Squamous cell papilloma (Skin)	Malignant lymphoma (Hematopoietic system)
Ras−HOL−	6.7%*	0%	60%
Ras+HOL−	87.5%	37.5%	50%
Ras−HOL+	0%	0%	55.6%
Ras+HOL+	62.5%	37.5%	75%

*Tumor incidence rate. Carcinogenicity test of 15 mice from each of the following offspring type: CB6F1-albino (Ras⁻HOL⁻), CB6F1-albino-rasH2 (Ras⁺HOL⁻), C6F1-albino-HOL (Ras⁻HOL⁺), and CB6F1-albino-rasH2-HOL (Ras⁺HOL⁺) were performed by administering N-methyl-N-nitrosourea. The mice that were alive at the end of the experimental period were necropsied, and systemic visual observations were performed.