Histopathological analysis
The gastric and esophogeal tissues were examined for histopathological changes at 33 weeks post exposure to MNNG. One slide containing two tissue sections from each of the 36 rats were prepared (Table 1). Tissues were fixed in 10% formalin solution and fixed overnight in cassettes. Each tissue section measured 1.5 x 0.3 x 0.1 cm in average. The paraffin-embedded tissues were sectioned on a microtome to 4 μm. The tissue sections were stained with hematoxylin-eosin (H&E) and examined by light microscopy to check for dysplasia and carcinoma. In addition, the cancer incidence and cancerous lesions were calculated as percentage of rats per group.