ID1 and breast cancer: Using the immortalized human mammary epithelial cells, Stankic and colleagues [5] showed that overexpression of ID1 can generate breast cancer cells with cancer stem cell (CSC)-like properties and that these cells were characterized by a high self-renewal capacity, enrichment in CD44high/CD24low expression, and an increased tumor-initiating potential by limiting dilution transplantation assay in vivo.