Staging Colorectal Cancer

Although colorectal cancer is often considered as a single entity, initial management and staging of colorectal cancers differ depending on whether the primary tumor is located in the rectum or the colon. The rectum is short (approximately 15 cm) and very close to other structures, with only a narrow margin of fat between the rectal wall and the mesorectal fascia. In addition, unlike the colon, there is no protective peritoneal lining surrounding the rectum. Furthermore, resection of rectal cancers is more challenging than that of colon cancers because of the complex anatomy in the pelvis and the proximity of the pelvic wall. As a result, the failure rate after surgery for locally advanced rectal cancers is greater than that for colon cancer. For example, the 5-year survival rate for stage IIIA cancers of the colon is 84%, compared with 56% for stage III cancers of the rectum. The strongest predictor of recurrence in rectal cancer is involvement of the mesorectal fascia. Therefore, it is critical to determine such involvement prior to treatment as well as other factors of staging, such as nodal involvement and distal metastases.