ABCB1 and acute lymphoblastic leukemia: These proteins are encoded by highly polymorphic genes (ABCB1 and ABCC5) that have been associated with increased ALL risk and have also been implicated in oncologic treatment interpatient variability (Gottesman et al., 2002; Brisson et al., 2015), specifically against anti-folate drugs (Wielinga et al., 2005), leading to an increased risk of relapse (Choi, 2005).