Overview of Rectal Cancer
Medically reviewed by Dr. C.H. Weaver M.D. Medical Editor 10/2018
The colon and rectum are parts of the body’s digestive system and together form a long, muscular tube called the large intestine. The colon is the first 6 feet of the large intestine and the rectum is the last 8-10 inches. The last part of the rectum contains the rectal sphincter or anus. The rectal sphincter is the muscle that controls defecation. Preservation of the rectal sphincter during surgery for rectal cancer is necessary in order to maintain control of bowel function. Treatment approaches differ between cancers of the colon or rectum, and are therefore discussed separately.
Adenocarcinoma is the most common type of cancer that originates in the cells that line the rectum or large intestine. It accounts for over 90-95% of cancers originating in the rectum. Other types of cancer including carcinoid and leiomyosarcoma also originate in the rectum, but are not referred to as rectal cancer. This treatment overview deals only with adenocarcinoma of the rectum, which will be referred to as rectal cancer.
The treatment of rectal cancer may involve several physicians, including a gastroenterologist, a surgeon, a medical oncologist, a radiation oncologist, and/or other specialists. Care must be carefully coordinated between the various treating physicians involved in management of your cancer.
Staging of Rectal Cancer
In order to understand the best treatment options available for treatment of rectal cancer, it is important to first determine where the cancer has spread in the body. The initial spread of rectal cancer occurs circumferentially around the rectum and laterally into the adjacent fat and muscles. Rectal cancer can then invade nearby organs and spread through the lymph and blood systems. Rectal cancer cells may spread via the blood throughout the body to the liver, lungs and other organs.
Determining the stage of the cancer or the extent of the spread requires a number of tests and is ultimately confirmed by surgical removal of the cancer and exploration of the abdominal cavity.
- Computerized Tomography (CT) Scan: A CT scan is a technique for imaging body tissues and organs, during which X-ray transmissions are converted to detailed images, using a computer to synthesize X-ray data. A CT scan is conducted with a large machine positioned outside the body that can rotate to capture detailed images of the organs and tissues inside the body. This method is more sensitive and precise than the chest x-ray.
- Magnetic Resonance Imaging (MRI): MRI uses a magnetic field rather than X-rays, and can often distinguish more accurately between healthy and diseased tissue. MRI gives better pictures of tumors located near bone than CT, does not use radiation as CT does, and provides pictures from various angles that enable doctors to construct a three-dimensional image of the tumor.
- Colonoscopy: A colonoscopy may be used to identify whether a second cancer is present in the colon or rectum prior to surgery. During a colonoscopy, a long flexible tube that is attached to a camera is inserted through the rectum, allowing physicians to examine the internal lining of the colon for polyps or other abnormalities. The physician may perform a biopsy during a colonoscopy in order to collect samples of suspicious tissues or cells for closer examination.
- Endorectal Ultrasound (EUS): Endorectal ultrasound (EUS) involves the use of a special probe that is inserted into the rectum to help determine the thickness of the cancer. By determining the thickness of the cancer, EUS can help determine the stage.
- Doppler Ultrasound: One technique that may help predict an increased risk of cancer recurrence is Doppler ultrasound. Doppler ultrasound has been used to measure blood flow in the artery to the liver (hepatic artery) and total liver flow in patients with rectal cancer. This measurement may be helpful because abnormalities occurring in hepatic artery blood flow can be used to detect early cancer metastasis to the liver.
Surgery for Rectal Cancer
Upon completion of the clinical “staging evaluation”, surgery is performed to remove the cancer, along with part of the normal adjacent tissues of the rectum. Surgery also helps to further determine the level of spread within the rectal wall and abdomen. The type of surgery performed depends on the size and the location of the cancer. Surgery is commonly performed through an abdominal incision. In some cases, the rectal cancer is located close to the anus and the anus is removed with the cancer.
Large rectal cancers close to the anus that cannot be removed without damaging anal function are sometimes treated with chemotherapy to help shrink the cancer before surgery. This is referred to as neoadjuvant chemotherapy. If there is enough shrinkage of the cancer, surgery may be performed that preserves anal function. However, in some cases, the cancer is too close to the anus and the anus is removed with the cancer.
In other instances, the cancer may be localized, but too large to remove surgically. In these cases, administration of chemotherapy and/or radiation before surgery may shrink the cancer and allow complete surgical removal.
Following surgical removal of rectal cancer, a final “pathologic” stage will be given. This is based on extent of spread of cancer after looking at the removed tissue under a microscope. The stage may be a letter or a number, as several different staging systems are used to describe rectal cancer. All new treatment information concerning rectal cancer is categorized and discussed by the stage. In order to learn more about the most recent information available concerning the treatment of rectal cancer, click on the appropriate stage.
Stage II (B2-3): Cancer may penetrate the wall of the rectum into the surrounding fat or muscles or other adjacent organs, but does not invade any local lymph nodes.
Stage III (C1-3): Cancer invades one or more of the local lymph nodes, but has not spread to other distant organs.
Stage IV (D): Cancer has spread to distant locations in the body, which may include the liver, lungs, bones or other sites.