The invention provides tissue culture system for primary cells (e.g. normal mammalian primary epithelial progenitors). This system includes: a) a serum-free, chemically defined cell culture media and, b) methods for isolation and in vitro long-term propagation of primary cells (e.g. primary epithelial cells). Primary cells so isolated and cultured can be kept undifferentiated and proliferate for many weeks (>15 weeks) or population doubling (>35 PD) without senescence, or any detectable genetic alterations. Upon changing media/culture conditions, these cells can be induced to differentiate.The invention also provides methods to transform normal primary cells so cultured into “cancer stem cells.” The genetically defined cancer stem cell tumor model mimics the behavior of the disease closely, e.g., the cells are invasive, hormone responsive and metastatic when injected into mice. The tumor cells express genes that are specific to cancer stem cells identified in patient samples.
