In general, the deeper the penetration, the worse the prognosis. Also, the involvement of local lymph nodes worsens prognosis. Figure 9 shows a cross-section of the bowel wall and different levels of invasion of colorectal cancer. Colorectal cancer that has been treated can come back at or close to the original site. If it does,it is referred to as a local recurrence.
Local recurrences are more common in rectal cancers than in colon cancers.
Colorectal cancer can also recur at a site distant to the original tumor. In that case, it is called a metastasis. The liver and lung are common metastatic sites of colorectal cancer. The polyp tissue is then sent to the pathology laboratory to confirm that cancer is present and to what degree the cancer may have penetrated the bowel wall. Depending on the pathology findings, subsequent surgery may be advisable.