UGT1A1 and Decreased total neutrophil count: Even, Innocenti F. et al. [44] comment that the toxicity profile of individualized irinotecan dosing does not change, highlighting that neutropenia is the dominant DLT, and diarrhea contributes to a lesser extent, and also that those ADEs are likely pharmacodynamic consequences of higher exposure to SN-38, which is in part determined by the UGT1A1*28 variant [55,56,57,58].