Palomaki et al. stated a few problems regarding the use of UGT1A1 in clinical practice; there seems to be a clear relationship between UGT1A1 genotype and severe neutropenia, but there is no direct or indirect evidence to support the clinical utility of modifying an initial and/or subsequent dose of irinotecan for patients with metastatic CRC as a way to change the rate of adverse drug events. This evidence concerns the gene UGT1A1 and neutropenia.