In particular, the link between the high expression of P-gp and poor clinical outcome has been reported in patients with metastatic breast cancer (MBC) (Kovalev et al., 2013) and blood cancers (Ross, 2000; Robey et al., 2018) such as chronic lymphocytic leukemia (CLL) (Matthews et al., 2006), chronic myeloid leukemia (CML) (Maia et al., 2018), and multiple myeloma (MM) (Schwarzenbach, 2002; Tsubaki et al., 2012). Here, PGP is linked to B-cell chronic lymphocytic leukemia.