CD44 and breast cancer: In a HER2-overexpressing breast cancer cell line, resistant to trastuzumab, the breast cancer-initiating CD44+/CD24-/low population was more sensitive to MTF treatment than the non-CD44+/CD24-/low population (estimated IC50 for MTF 1 ± 0.2 mM vs. 11 ± 2 mM) [99].