We analyzed the morphological changes accompanying the development of cancer in the mouse forestomach. The main aim of the study was to evaluate whether cancer in this area of the stomach arises de novo or undergoes a series of precancerous changes. Tumors were induced by the 1,2-dimethylbenz(a)antracene (DMBA) at a total dose of 4 mg/mouse. The suspected areas of the stomach were studied morphologically in 79 mice. Benign tumors (squamous-cell papillomas) and malignant tumors (squamous-cell carcinomas) were found in 40 mice. Tumors arose in all cases together with differential changes in the forestomach epithelium. These changes were seen as irregular diffuse hyperplasia or focal proliferation, with or without differential signs of dysplasia. Destruction of the basal epithelial membrane indicated transformation of the process into malignant invasive carcinoma. Thus, in chemically induced cancer of the forestomach, squamous-cell carcinoma develops as the final stage of morphologically recognizable precancerous changes in the epithelial layer. De novo formation of such tumors in the forestomach was not observed.

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