CD44 and cancer: In addition, etoposide decreased CSC (CD44+CD24+ALDH1+) frequency in the CSC populations (Fig. 6c, left), which is indicative of its CSC-targeting cytotoxic activity39, and reduced CSCs’ PD-L1 expression (Fig. 6c, right), suggesting that etoposide effectively modulates PD-L1 expression in both CSC and non-CSC populations of mesenchymal-like cancer cells.