It should be noted that the potential contribution of CD44 to the maintenance of higher levels of ROS metabolism in CSCs than in normal cells is of increasing interest, as lower levels of ROS are found in subpopulations of CSCs in human and murine mammary tumors compared to the corresponding non-tumorigenic cells, and hyaluronan/CD44s-mediated activation of NRF2 may be a programming mechanism for enhanced ROS defense in CSCs (27). This evidence concerns the gene CD44 and breast cancer.