These results show that even though well-established breast cancer cell lines express specific stem/progenitor cell-like protein markers, the 10AT-Her2 cell population can be considered to have a more enhanced ‘stemness’ character because of its highly efficient tumorsphere-formation property (Figure 2B), and as discussed in later sections, its ability to form tumor xenografts at low cell numbers in athymic mice. This evidence concerns the gene ERBB2 and neoplasm.