A total of 132 metastatic colorectal cancer patients were genotyped for CYP3A4*1B, CYP3A4*18, CYP3A5*3, DPYD*2A, DPYD*5, DPYD c.1774C > T, UGT1A1*28, UGT1A1*6, ABCB1 c.1236C > T, ABCB1 c.3435C > T, ABCC2 c.3972C > T, and ABCG2 c.421C > A. This evidence concerns the gene UGT1A1 and metastatic colorectal cancer.