Interactions between normal mammary epithelial cells and mammary tumour cells in a model system.

Normal mammary epithelial (NME) cells and MCF-7 cells aggregate and grow as spheroids when cultured on extracellular matrix derived from Engelbreth/ Holmes/Swarth (EHS) tumour. NME cells stop dividing and differentiate but MCF-7 cells continue to proliferate, although growth is counterbalanced by cell death. In mixed cultures of NME cells and MCF-7 cells, the two cell types form mixed aggregates but then segregate to form well separated domains, often joined by only a narrow neck of cells. In these mixed cultures the growth of MCF-7 cells is inhibited by a factor secreted by NME cells into the medium.