UGT1A1 and colorectal cancer: Consequently, we conducted the first prospective multicenter phase II study in Japan to investigate the efficacy and safety of FOLFIRI plus bevacizumab regimen with the irinotecan dose set to 180 mg/m2 in compliance with Good Clinical Practice (GCP) guidelines in patients with advanced or recurrent colorectal cancer who were of the wild-type or heterozygous group for UGT1A1*28 and *6 polymorphisms and had discontinued oxaliplatin-based regimen.