ALDH1A1 and breast cancer: Surprisingly, these theoretical data, concerning a single niche, are strongly similar to the experimental data found in the mammary tumor mass, namely: 0.084% for ALDH1+ CD44+ Ki67+ CSCs (hypothetical CSC1s); 5.54% for ALDH1+ CD44– Ki67+ CSCs (hypothetical CSC2s); 12.87% for ALDH1– CD44+ Ki67– CSCs (hypothetical CSC3s); and 18.494% for total CSCs (Liu et al., 2014).