For Prevention of Diarrhea in Patients Diagnosed With Metastatic Colorectal Cancer Treated With Chemotherapy

Inclusion Criteria: * Diagnosis of colorectal cancer (either newly diagnosed or recurrent disease) with evidence of metastatic disease and present or past histological documentation of adenocarcinoma of the colon or rectum. * Tumor must be measureable. * Resolution of all acute toxic effects of any prior radiotherapy or surgical procedure. * ECOG performance status 0 or 1. Age \>= 18 years. * Required baseline laboratory. * Negative pregnancy test. * Willingness and ability to comply with the treatment plan. Exclusion Criteria: * Current enrollment in another clinical trial. * Prior adjuvant therapy for colorectal cancer \<= 6 months prior to randomization. * Prior systemic anticancer therapy or intra-arterial cytotoxic chemotherapy given as treatment for metastatic colorectal cancer. * Known allergy to CPT-11, 5-FU, LV, celecoxib, other COX-2 inhibitors, non-steroidal anti-inflammatory drugs (NSAIDS), salicylates, or sulfonamides. * Chronic concomitant use of full-dose aspirin, other NSAIDs or other COX-2 inhibitors for a chronic nonmalignant condition. * A requirement for chronic concomitant use of low-dose (cardioprotective) aspirin. * Chronic oral steroid use for treatment of a non-malignant condition. * Known ulceration of the gastric or duodenal mucosa \<= 30 days prior to randomization. * Need for concomitant fluconazole or lithium. * Any known significant bleeding disorder. * Active inflammatory bowel disease or chronic diarrhea.