Proto-neoplasia revisited: the molecular biology of mouse mammary hyperplasia.

The mouse mammary tumor model is a well characterized multistep tumor system which has been used to study characteristics of protoneoplastic and neoplastic lesions of the breast. The ability to transplant mammary epithelial tissue or cells into gland cleared fat pads makes this system more powerful and versatile than most tumor models. Transplantability has provided sufficient tissue to allow sequential molecular analysis of protoneoplastic tissue, making studies of clonality and oncogene activation during tumorigenesis possible. It has also been extensively used for the study of a wide range of carcinogenic agents. The recent development of transgenic mice and transgenic mammary gland technologies provide exciting new avenues of research by providing the opportunity for prospective in-vivo studies of carcinogenesis.