Despite the dose reduction we applied, we observed a numerically higher rate of severe neutropenia in patients with homozygous polymorphisms in the UGT1A1 gene (*28/*28) when compared to heterozygous or wild-type genotypes (*1/*1 or *1/*28 allele carriers) with and without dose reduction. The gene discussed is UGT1A1; the disease is Decreased total neutrophil count.