OUTLINE: This is a multicenter study. Patients are stratified according to best response during first-line chemotherapy/bevacizumab treatment (complete response and partial response vs stable disease), duration of first-line treatment (16-20 weeks vs 21-24 weeks), type of chemotherapy used during first-line treatment (irinotecan and fluoropyrimidine vs oxaliplatin and fluoropyrimidine vs fluoropyrimidine monotherapy), disease burden (one organ with metastasis vs more than one organ with metastasis), and by participating center.