Effects of CPLA on the expression of β-catenin in rat esophageal NMBA-induced tumorigenesis. Legend: A, normal control; B, soya oil control; C, CPLA and NMBA group; D, NMBA control group. *P<0.05 compared with the NMBA control group; #P<0.05 compared with the normal control group. CPLA, lupeal acetate of Cortex periplocae; NMBA, N-nitrosomethyl-benzylamine; IOD, integrated optical density.