Cancer of the Colon and Rectum
Comprised of more than one hundred different diseases, cancer affects the body's basic unit, the cell. In a healthy body, cells divide to produce additional cells when they are required.
When cells become abnormal and begin to divide without sense or order – when the body has no need for new cells – cancer occurs. This out-of-control cell division results in a mass of excess tissue called a growth or tumor. Growths that are malignant – capable of spreading to other parts of the body – are referred to as cancer.
Colon cancer – also known as colorectal cancer – is cancer that begins in the cells of the colon (sometimes referred to as the large intestine), or the rectum. While there are other types of cancer that attack the colon, generally the term colon cancer refers to colon carcinoma (rather than rare types of colon cancer such as carcinoid tumors, lymphoma, melanoma, and sarcomas).
What Causes Colon Cancer?
While there is no single cause for colon cancer, some people are more likely to develop colorectal cancer than others.
Most colon cancers begin as benign polyps that develop into cancer over time. Factors that increase a person's risk of developing colorectal cancer include a family history of colon cancer and polyps, presence of polyps in the colon, chronic ulcerative colitis, and high fat intake.
Other risk factors include,
- Cancer elsewhere in the body
- Crohn's disease
- Personal history of breast cancer
Among first-degree relatives of colon cancer patients, the lifetime risk of developing colon cancer is eighteen percent (three times that of the general population in the United States).1 However, eighty percent of colon cancers develop sporadically in patients with no family history of colon cancer.2
While colon cancer is rare in Asia and Africa, the incidence is on the increase in countries where people have adopted western diets. Though colorectal cancer is normally associated with a high-fat, low-fiber diet and red meat, some studies indicate that the risk does not decrease if a high-fiber diet is implemented, making the cause of this link unclear.3
What Are the Symptoms of Colon Cancer?
Colorectal cancer can be present for years prior to the development of symptoms. Symptoms are numerous and non-specific. Conditions such Crohn's disease, diverticulosis, irritable bowel syndrome (IBS, also known as spastic colon), peptic ulcer disease, and ulcerative colitis can have similar symptoms. And, many colon cancer cases have no symptoms.
However, the following symptoms may be colon cancer indicators:
- Abdominal pain and tenderness in the lower abdomen
- Change in bowel habits
- Intestinal obstruction
- Narrow stools
- Red or dark blood in stool
- Shortness of breath
- Unexplained anemia
- Weight loss with no known reason
Right-sided or Left-sided Colon Cancer
Symptoms can vary depending on the location of a tumor. The right colon is spacious. Accordingly, cancers of the right colon (ascending colon and cecum) tend to grow outwards from one location in the bowel wall. They can become quite large before causing any abdominal symptoms.
Right-sided cancers typically cause iron deficiency anemia, leading to fatigue, weakness, and shortness of breath. Rarely do right-sided cancers obstruct feces.
The left colon is narrower than the right colon. As a result, cancers of the left colon tend to develop around the colon, and can obstruct the bowel the way a napkin ring would.
Left-sided cancers present with symptoms such as constipation, narrowed stool, diarrhea, abdominal pains, cramps, and bloating. Blood in the stool may also be symptomatic of a growth near the end of the left colon or rectum.
Diagnosis and Screening
Colon cancer is most curable when it is detected before the onset of symptoms. For individuals who are at increased risk, there are various diagnostic tests available.
- Blood tests – measurement of the patient's blood for elevated levels of certain proteins gives an indication of tumor load
- Colonoscopy – a lighted probe inserted in the rectum and entire colon checks for polyps and other abnormalities; polyps can be immediately removed during this exam, and tissue can be removed for biopsy
- Digital rectal exam (DRE) – detects tumors large enough to be felt in the distal part of the rectum with a gloved finger
- Double contrast barium enema (DCBE) – a thin layer of barium over the inner lining of the colon gives the intestine a white appearance, and any polyps would appear dark by contrast on X-ray film
- Fecal occult blood test (FOBT) – tests for blood in the stool
- Genetic counseling and testing – screens for families who may have a hereditary form of colon cancer
- Positron emission tomography (PET) – a three-dimensional scanning technology using injected, radioactive sugar to produce an image
- Sigmoidoscopy – a lighted probe inserted in the rectum and lower colon checks for polyps and other abnormalities
- Standard computed axial tomography (CT or CAT scans) – an X-ray method used to determine the degree of spread of cancer
- Stool DNA testing – an emerging technology in screening for colorectal cancer
- Virtual colonoscopy – similar to a DCBE, except that a special computed tomography scan is used instead of X-ray film
- Whole-body PET imaging – the most accurate, cost-effective diagnostic test for detection of recurrent colorectal cancer
If initial screening indicates colorectal cancer, additional tests will need to be performed. Known as staging, this testing determines the degree to which the cancer has spread:
Stage 0: Early cancer on the innermost layer of the intestine
Stage I: Cancer is in the inner layers of the colon
Stage II: Cancer has spread through the muscle wall of the colon
Stage III: Cancer has spread to the lymph nodes
Stage IV: Cancer has spread to other organs
Treatment and Prognosis
Colorectal cancer is the third most common cancer in the United States. The American Cancer Society estimates that there will be about 112,340 new cases of colon cancer and 41,420 new cases of rectal cancer in 2007. Combined, they will cause about 52,180 deaths.4
However, in almost all cases, early diagnosis can lead to a complete cure. When treated at an early stage, more than ninety percent of patients survive at least five years after their diagnosis.5
Dependant partly on the stage of the cancer, treatments generally include
- Chemotherapy to kill cancer cells
- Surgery to remove cancer cells
- Radiation therapy to destroy cancerous tissue
Increased awareness, including screening by colonoscopy, is thought to be the reason for the drop in the death rate from colon cancer in the last fifteen years.6 Accordingly, it is recommended that men and women fifty and older have a colonoscopy.
Yearly digital examinations of the rectum and stool occult blood testing are recommended for those over the age of forty. Tumors of the colon and rectum tend to bleed slowly into the stool, but the blood is not usually visible to the naked eye.
A person who tests positive for stool occult blood has a thirty to forty-five percent chance of having a colon polyp and a three to five percent chance of having colon cancer.7
Beginning at age fifty, a flexible sigmoidoscopy screening test is recommended every three to five years. If a polyp or cancer is found, a complete colonoscopy is recommended.
Blood tests are available to test for the genetic colon cancer syndromes hereditary nonpolyposis colorectal cancer (HNPCC), familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), and MYH gene-associated polyposis (MAP).
Dietary and lifestyle modifications are important. While not conclusive, some evidence suggests that a low-fat, high-fiber diet may reduce the risk of colon cancer.
In addition, reducing red meat consumption is believed to lower the chance of colorectal cancer. In 2005, the Journal of the American Medical Association concluded a long-term study of nearly 149,000 red meat eating adults.
The participants who ate the most red meat were thirty to forty percent more likely to develop colon cancer than those who ate the least. Further, participants who ate more processed meats were fifty percent more likely to develop colon cancer, and twenty percent more likely to develop rectal cancer compared to those who ate the least.8
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1. Dennis Lee, MD and Jay Marks, MD, MedicineNet.com, "Colon Cancer (Colorectal Cancer)," MedicineNet.com http://www.medicinenet.com/colon_cancer/article.htm (accessed December 2, 2007).
3. Mediline Plus, Medical Encyclopedia, "Colon cancer," United States National Library of Medicine and National Institutes of Health,
http://www.nlm.nih.gov/medlineplus/ency/article/000262.htm (accessed December 2, 2007).
4. American Cancer Society, "Colon and Rectum Cancer,"
How_Many_People_Get_Colorectal_Cancer.aspx?sitearea= (accessed December 2, 2007).
5. Mediline Plus, Medical Encyclopedia, "Colon cancer," United States National Library of Medicine and National Institutes of Health,
http://www.nlm.nih.gov/medlineplus/ency/article/000262.htm (accessed December 2, 2007).
7. Dennis Lee, MD and Jay Marks, MD, MedicineNet.com, "Colon Cancer (Colorectal Cancer)," MedicineNet.com http://www.medicinenet.com/colon_cancer/article.htm (accessed December 2, 2007).
8.American Cancer Society, ³Eating Lots of Red Meat Linked to Colon Cancer,²
Red_Meat_Linked_to_Colon_Cancer.asp (accessed December 19, 2007).