Colorectal cancer is categorized by stages from stage 0 to stage IV. For stages 0 through III, surgery is necessary to remove the tumor. For stages II and above, chemotherapy and/or radiation my also be used to treat the cancer. Stages I through IV are also classified as Dukes A through D stages. Follow the links below to find WebMD's comprehensive coverage about how colorectal cancer is classified, treatment by stages, and much more.