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Colorectal Cancer
The colon and the rectum
The colon and rectum are part of the large intestine (large bowel) which is located in the abdomen between the small intestine and the anus. Colon and rectum cancers, which are sometimes referred to together as “colorectal cancer,” arise from the lining of the large intestine. When cancer arises from the lining of an organ like the large intestine, it is called a carcinoma.
The colon absorbs water, electrolytes, and nutrients from food and transports them into the bloodstream. It is about 6 feet in length and consists of the cecum, the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. The rectum is the last segment of the large intestine. It is 8 to 10 inches in length and leads to the anus, which is the opening to the outside of the body. Waste material is stored in the rectum until it is eliminated from the body through the anus.
What Is Colorectal Cancer?
Colorectal cancer is a term used to refer to cancer that starts in the colon or rectum. Colon and rectal cancers begin in the digestive system, also called the GI (gastrointestinal) system. This is where food is processed to create energy and rid the body of waste matter. The colon has 4 sections. Cancer can start in any of the four sections or in the rectum. The wall of each of these sections (and rectum) has several layers of tissues. Cancer starts in the inner layer and can grow through some or all of the other layers. Knowing a little about these layers is helpful because the stage (extent of spread) of a cancer depends to a great degree on which of these layers it affects. Cancer that starts in the different areas may cause different symptoms. In most cases, colon and rectum cancers develop slowly over a period of several years.
What Causes Colorectal Cancer?
While we do not know the exact cause of most colorectal cancer, there are certain known risk factors. A risk factor is something that increases a person’s chance of getting a disease.
Diet: A diet high in fat, especially fat from animal sources, can increase the risk of colorectal cancer.
Lack of exercise: People who are not active have a higher risk of colorectal cancer.
Alcohol: Heavy use of alcohol has been linked to colorectal cancer.
Having had colorectal cancer before: Even if a colorectal cancer has been completely removed, new cancers may start in other areas of your colon and rectum.
Bowel diseases: People who have had ulcerative colitis or Crohn’s disease for a long time also have an increased risk of developing bowel cancer during their lifetime. Ulcerative colitis and Crohn’s disease are diseases of the lining of the bowel.
What are the symptoms of colon cancer?
Most cases of colon cancer have no symptoms. The following symptoms, however, may indicate colon cancer:
- Diarrhea, constipation, or other change in bowel habits that does not resolve
- Blood in the stool
- Unexplained anemia (anemia in any adult who is not a menstruating woman should almost always be evaluated by a colonoscopy)
- Abdominal pain and tenderness in the lower abdomen
- Intestinal obstruction
- Weight loss with no known reason
- Stools narrower than usual
What about the Treatment ?
Treatment depends partly on the stage of the cancer. This means how far the tumor has spread through the layers of the intestine, from the innermost lining to outside the intestinal wall and beyond:
- Stage 0: Very early cancer on the innermost layer (more accurately considered a precursor to cancer)
- Stage I: Tumor in the inner layers of the colon
- Stage II: Tumor has spread through the muscle wall of the colon
- Stage III: Tumor that has spread to the lymph nodes
- Stage IV: Tumor that has spread to distant organs
Stage 0 colon cancer may be treated by cutting out the lesion, often via a colonoscopy. For stages I, II, and III cancer, more extensive surgery to remove a segment of colon containing the tumor and reattachment of the colon is necessary. This procedure only rarely requires a colostomy.
Almost all patients with stage III colon cancer, after surgery, should receive chemotherapy (adjuvant chemotherapy) with a drug known as 5-fluorouracil given for approximately 6 - 8 months. This drug has been shown to increase the chance of a cure. There is some debate as to whether patients with stage II colon cancer should receive chemotherapy after surgery, and patients should discuss this with their oncologist.
Chemotherapy is also used for patients with stage IV disease in order to shrink the tumor, lengthen life, and improve the patient’s quality of life. Irinotecan, oxaloplatin, and 5-fluorouracil are the 3 most commonly used drugs, given either individually or in combination. There are oral chemotherapy drugs which are similar to 5-fluroruracil, the most commonly used being capecitabine (Xeloda).
Oxaliplatin, a newer chemotherapy drug, was approved by the FDA in 2002 and is also active against colon cancer. It is often used in combination with 5-fluorouracil, and studies are being done that combine it with other chemotherapy drugs. Other chemotherapy agents, including drugs that specifically target abnormalities in cancer cells, are currently in development and undergoing clinical trials.
For patients with stage IV disease that is localized to the liver, various treatments directed specifically at the liver can be used. Tumors may be surgically removed, burned, or frozen in some cases. Chemotherapy or radioactive substances can sometimes be infused directly into the liver.
Radiation therapy is occasionally used in patients with colon cancer, but this is often used in combination with chemotherapy for patients with stage III rectal cancer.
Colorectal cancer sites
- MedlinePlus: Colorectal Cancer - US National Library of Medicine compilation which provides links to select related subjects.
- Colon Cancer Network - Colon cancer support. Volunteer opportunties to end colon cancer. We serve all communities that are touched by colorectal cancer. Preventable, Treatable …
- Colon Cancer Alliance - Support and Information for People Affected by Colorectal Cancer.
- National Colorectal Cancer Awareness Month - March 2002 begins the third annual nationwide effort to educate the public about steps that can protect against colorectal cancer and reduce the number of …
- American Cancer Society - The Cancer Experience: Colon and Rectum Cancer. The 12-part Cancer Experience series offers specific information on how to cope with cancer, every step of …
