To generate a mammary epithelial cancer cell system highly enriched with tumor-initiating cells that express high levels of nucleostemin, preneoplastic MCF-10AT human mammary epithelial cells [18–20] were stably transfected with either the CMV-HER2 expression vector containing the neomycin resistance gene, or the control CMV-neomycin resistance gene vector forming 10AT-Her2 and 10AT-Neo cells, respectively. The gene discussed is ERBB2; the disease is neoplasm.