<b>Methods:</b> We retrospectively analyzed 147 patients with unresectable metastatic colorectal cancer (mCRC) treated with first-line FOLFIRI-3 between 2005 and 2020 who underwent <i>UGT1A1</i> genotyping for *6 and *28 variants. The gene discussed is UGT1A1; the disease is metastatic colorectal cancer.