ABCB1 and neutropenia: More recently, Salvador-Martín et al. analyzed the association between variants in ABC efflux transporter genes and irinotecan adverse effects, and found that the ABCB1 variants were significantly associated with overall toxicity (P<0.01) and with higher hematological toxicity including, but not limited to, neutropenia (P<0.01) (Salvador-Martín et al., 2018).