Patients with stage 0 and I disease are typically treated with surgery only. Patients with stage II and III disease are at a high risk of recurrence and should be treated with chemotherapy and radiation either pre- (called neoadjuvant therapy) or post-operatively (called adjuvant therapy). Studies have shown that giving fluorouracil (5-FU) in combination with radiation therapy (called chemo radiation) is more effective than radiation alone. Due to the large size of the pelvis (the bony structure in which the rectum lies), it is often difficult for a surgeon to remove enough normal surrounding tissue to obtain adequate tumor-free margins. This is especially true for larger tumors. Giving chemo radiation pre-operatively can shrink a tumor that would not have been surgically removable initially, therefore making these patients candidates for potentially curative surgery. This is known as "down staging" the tumor. Down staging with chemo radiation has also allowed patients with tumors that would otherwise require a colostomy to now have a resection and anastomosis following treatment. In addition, chemo radiation, either before or after surgery, has shown significant improvement in survival for these patients.
