Carcinoma of the colon and rectum usually develops in older patients, but some people do get tumors early in life. Most tumors develop from benign polyps, which undergo malignant change. As the malignancy develops it invades through the wall of the bowel and then metastasizes to local lymphatics. The tumor extends within the wall for a few centimeters above and below its origin. Lymphatic spread is to local and regional lymph nodes and then to the pre-aortic lymph node chain. These drain eventually into the thoracic duct.