In addition, UGT1A1*6 was significantly associated with grade 1–4 and severe neutropenia (grade 3–4) (OR 20.3, 95% CI 4.3–95.6; P < 0.001, and OR 4, 95% CI 1.2–13; P < 0.026, respectively). Here, UGT1A1 is linked to neutropenia.