The invention is directed to a transgenic non-human mammal with constitutive, tissue-specific cytokine expression and the use of the transgenic mammal as a model for spontaneous development of cancer. Particularly, the invention provides for a transgenic mouse where specific expression of interlueukin-1.beta. in the stomach results in the development of gastric cancer. The invention also encompasses methods using the transgenic mammals for screening compounds for their ability to modulate the development, growth or progression of cancer.