GSTP1 and neoplasm: GSTP1 knock-out mice treated with the polycyclic aromatic hydrocarbon 7,12-dimethylbenz anthracene and the tumor promoting agent 12-O-tetradecanoylphorbol-13-acetate show increased numbers and earlier onset of skin papillomas demonstrating that loss of expression of a single GST can contribute to carcinogenesis [45].