Normal mammary homeostasis, and by implication tumorigenesis, are dependent upon the dynamic interplay between epithelial cells, stromal components and the extracellular matrix. To study the evolution of human breast cancer, a functionally relevant cell culture model is required which recognizes the complexity of the mammary gland's microenvironment. The development of an appropriate breast epithelial cancer cell model will be dependent on the ability to recreate the 'normal' and 'neoplastic' tissue microenvironment in culture. Towards this goal, a 3-dimensional extracellular matrix (ECM) assay, employing a reconstituted basement membrane, has been developed which allows for the rapid and accurate discrimination of normal and neoplastic cells when cultured. To investigate stromal/epithelial cell interactions, we have developed a tumor environment assay which essentially mirrors the tumor microenvironment histologically. The use of a novel, near diploid, human breast epithelial cell line, HMT-3522, which has transformed spontaneously with passage in culture, together with these 3-dimensional culture assays is expected to provide meaningful markers of initiation and progression.