There was a higher instance of neutropenia in patients receiving nal‐IRI+5‐FU/LV who had mutations in UGT1A1 (homozygous for UGT1A1*6 [n =2] or heterozygous for UGT1A1*6 and UGT1A1*28 [n =1]). This evidence concerns the gene UGT1A1 and neutropenia.