Multivariate analysis identified a low baseline white blood cell count (odds ratio [OR], 14.50; 95% confidence interval (CI), 3.27–111.14; p = 0.002) and presence of heterozygosity for UGT1A1*28 or UGT1A1*6 polymorphism (OR, 2.84; 95% CI, 1.18–7.17; p = 0.023) as independent risk factors for severe neutropenia. This evidence concerns the gene UGT1A1 and neutropenia.