[Diagnosis and staging of colorectal cancers].

Early colorectal cancer produces no symptom, thus justifying efforts at detection in screening programs. Symptoms are usually secondary to obstruction, local invasion, perforation or bleeding. Any fecal bleeding must be investigated to rule out a colorectal cancer. The initial imaging study to identify a colorectal cancer is often colonoscopy, which is frequently supplemented with a double contrast barium enema. Once the presence of cancer is histologically proven, the preoperative evaluation includes detection of hepatic and extrahepatic spread, especially with ultrasound and CT scan. Endorectal ultrasonography has been shown to be a significant advance for staging rectal cancer. It provides the best staging in selecting patients for preservation of sphincter function and for adjuvant therapies. The most useful prognostic factors in tumors without distant metastases are the depth of tumor extension, the number of positive lymph nodes and the histologic grade. Preoperative CEA level, vascular invasion and ploidy are also important prognostic factors.