Species Spontaneous Carcinogen exposure* Human 10-10 10-6/-7 Mouse 10-5 10-3/-4 Rat 10-6 10-4 Syrian hamster 10-9 10-6/-7 Chinese hamster 10-6 10-4

Table 1: Relative propensities of fibroblasts from different mammalian species to spontaneous- or carcinogen-induced immortalization. The efficacy of carcinogen-induced immortalization is dependent on the specific carcinogen and the doses. Here, an estimation of immortalization efficacy for a variety of carcinogens and doses is provided.