CD44 and breast cancer: After detecting the expression of CD44, CD24, and ALDH1 of CTCs in 30 metastatic breast cancer patients, Theodoropoulos et al. found that 35.2% of 1439 CTCs were CD44+/CD24-/low, and 17.7% of 238 CTCs were ALDH1high/CD24-/low, providing evidence of CTCs stemness96.