Incidence of Spontaneous and Urethane-Induced Tumors in a 26-Week Carcinogenicity Study in Tg.rasH2 Mice Sourced From CLEA, Japan

The Tg.rasH2 mouse is a validated bioassay system for evaluation of carcinogenic potential, and it is confirmed to be sensitive to both genotoxic and nongenotoxic carcinogens. This is also one of the models specified in ICH S1B Guidance, enabling 6-month carcinogenicity studies as an alternative to traditional 2-year bioassays. We conducted a 26-week carcinogenicity study at our test facility on Tg.rasH2 mice sourced from CLEA Japan Inc., in a process to generate historical control database. Although historical control data have been published for these mice sourced from Taconic Biosciences Inc., USA, there is a dearth of published literature citing spontaneous incidence of neoplastic findings in Tg.rasH2 mice sourced from CLEA Japan. We have therefore presented the spontaneous tumor incidence in our study and compared it with the previously published tumor incidence for Tg.rasH2 mice sourced from Taconic, USA. The comparison reveals a similarity of tumor incidence between the mice from these two sources.