Male and female adult E6/E7 transgenic mice and age matched nontransgenic control mice received topical treatments of DMBA (dimethylbenz[a]anthracene) dissolved in 100% DMSO (dimethylsulfoxide) to the anal canal once per week for twenty weeks. Treatments were initiated between 5 and 7 weeks of age. Prior to topical treatment, the mouse anal canal was evacuated of feces using manual, external pressure to the pelvic brim. Mice were treated with 0.12, 0.04 or 0.012 μmoles DMBA or DMSO without DMBA. All treatments had 4 μL of liquid inserted 5-10mm into the anal canal using a standard pipette tip. After twenty weeks of treatment, mice had an eight-week hiatus before being euthanized and anal tissue harvested for histological analysis. Mice were monitored weekly for appearance of overt tumors though only overt tumors present at sacrifice were included in the tumor phenotype data (Table 2). Overt tumors were defined as any neoplastic lesion in the anal region capable of being seen by the examiner's naked eye that proved to be a tumor upon histopathological assessment, regardless of disease classification (papilloma, atypia, carcinoma). Overt tumor size (diameter in mm) was measured at the time of sacrifice.