Antimetabolites, Antineoplastic/therapeutic use; Antineoplastic Agents/therapeutic use; Antineoplastic Combined Chemotherapy Protocols/therapeutic use; Camptothecin/analogs & derivatives; Colorectal Neoplasms/drug therapy; Drug Resistance, Neoplasm/genetics; Fluorouracil/therapeutic use; Proto-Oncogene Proteins/genetics; ras Proteins/genetics; Aged; Antibodies, Monoclonal/administration & dosage; Antineoplastic Agents/administration & dosage; Antineoplastic Agents/adverse effects; Antineoplastic Combined Chemotherapy Protocols/adverse effects; Camptothecin/administration & dosage; Camptothecin/adverse effects; Camptothecin/therapeutic use; Chi-Square Distribution; Colorectal Neoplasms/enzymology; Colorectal Neoplasms/genetics; Colorectal Neoplasms/mortality; Colorectal Neoplasms/pathology; DNA Mutational Analysis; Disease-Free Survival; Drug Administration Schedule; ErbB Receptors/antagonists & inhibitors; ErbB Receptors/metabolism; Female; Humans; Irinotecan; Male; Middle Aged; Mutation; Panitumumab; Proportional Hazards Models; Prospective Studies; Proto-Oncogene Proteins p21(ras); Time Factors; Treatment Outcome; United Kingdom