Human models of breast cancer.

Experimental systems using human mammary tissue, secretions and tumours may be based on in vitro culture or on growth of tissue or tumour fragments in the nude mouse. In the development of in vitro culture systems, a detailed characterization of the cultured cells within the framework of the epithelial cell lineages found in vivo is crucial. Monoclonal antibodies are useful tools for defining the profile of antigens expressed by the basal and luminal cells in the normal gland and in distinguishing subclasses between these two major groups. When these same reagents are used to characterize breast cancers, the majority are found to show the phenotype of luminal cells, with a small subset showing some evidence of basal markers. Luminal epithelial cells cultured from milk or reduction mammoplasty tissue have a short life span in vitro but can be immortalized using SV40TAg. Demonstrably malignant cells are difficult to culture from primary breast cancer, but ER+ and ER- cell lines showing the luminal phenotypes have been readily developed from metastases: some ER- breast cancer cell lines show a more undifferentiated phenotype, and these may have developed from tumours expressing basal markers. As with in vitro culture, it is difficult to obtain tumour growth in the nude mouse from primary breast cancer specimens, and established cell lines are also difficult to grow in this animal. We have focused our studies on cell lines with the luminal phenotype developed from milk. These non-tumorigenic cell lines differ from breast cancer cell lines (a) in being able to form organized three dimensional structures in the presence of an extracellular matrix and (b) in the correct glycosylation of the polymorphic epithelial mucin, which is expressed and aberrantly glycosylated in cancers. These cell lines are therefore being used to study the mechanisms underlying morphogenesis and the processing of PEM, and also as recipients for oncogenes and proto-oncogenes.