What is colon cancer?

Colon cancer (or colorectal cancer or large bowel cancer) is cancer that starts in the large intestine (colon) or the rectum (end of the colon). Tumors of the colon and rectum are growths arising from the inner wall of the large intestine.

It is the third most common form of cancer and the second leading cause of cancer-related death in the Western world. Colorectal cancer causes 655,000 deaths worldwide per year, including about 16,000 in the UK, where it is the second most common site (after lung) to cause cancer death.

Causes or risk factors of colon cancer

Colorectal cancer is one of the leading causes of cancer-related deaths in the United States. However, early diagnosis often leads to a complete cure.

Nearly all colon cancers begin as non-cancerous (benign) polyps, which slowly develop into cancer.

Though there is no single cause for colon cancer, you are at a higher risk for this type of cancer if you have:
•  Cancer elsewhere in the body
•  Colorectal polyps
•  Personal history of breast cancer
•  Crohn's disease
•  Family history of colon cancer
•  Ulcerative colitis
•  Certain genetic syndromes
•  Smoking cigarettes

Signs and symptoms of colorectal cancer

The first symptoms of colon cancer are usually vague, like weight loss and fatigue (tiredness). Local (bowel) symptoms are rare until the tumor has grown to a large size. Generally, the nearer the tumor is to the anus, the more bowel symptoms there will be.

The following symptoms may indicate colorectal cancer:
•  Diarrhea, constipation, or other change in bowel habits
•  Unexplained weight loss
•  Abdominal pain and tenderness in the lower abdomen
•  Intestinal obstruction
•  Bloody stools or rectal bleeding
•  Narrow stools
•  Anemia, causing dizziness, fatigue and palpitations

You must call your health care provider if you have:
•  Black, tar-like stools
•  Blood during a bowel movement
•  Change in bowel habits

Diagnosis and screening

Colorectal cancer can take many years to develop and early detection of colorectal cancer greatly improves the chances of a cure. Therefore, screening for the disease is recommended in individuals who are at increased risk. There are several different tests available for this purpose.

Following are some of the screening methods used:
•  Digital rectal exam (DRE)
•  Fecal occult blood test (FOBT)
•  Endoscopy (Sigmoidoscopy or Colonoscopy )
•  Double contrast barium enema (DCBE)
•  Virtual colonoscopy with a special computed tomography scan
•  Standard computed axial tomography
•  Blood tests
•  Genetic counseling and genetic testing
•  Positron emission tomography (PET)
•  Whole-Body PET imaging
•  Stool DNA testing

If your doctor learns that you do have colorectal cancer, more tests will be done to see if the cancer has spread. This is called staging .

Stage 0: Very 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 that has spread to other organs

Treatment

Treatment options depend on the following:
•  The stage of the cancer
•  Whether the cancer has recurred
•  The patient’s general health

When colorectal cancer is caught at early stages (with little spread) it can be curable. However when it is detected at later stages (when distant metastases are present) it is less likely to be curable.

Treatments may include:
•  Chemotherapy to kill cancer cells
•  Surgery to remove cancer cells
•  Radiation therapy to destroy cancerous tissue

Stage 0 colon cancer may be treated by removing the cancer cells, often during a colonoscopy . For stages I, II, and III cancer, more extensive surgery is needed to remove the part of the colon that is cancerous. Almost all patients with stage III colon cancer should receive chemotherapy after surgery for approximately 6 - 8 months. Chemotherapy is also used to treat patients with stage IV colon cancer. For patients with stage IV disease that has spread to the liver, various treatments directed specifically at the liver can be used.

Prevention

The death rate for colon cancer has dropped in the last 15 years. This may be due to increased awareness and screening by colonoscopy .

Colon cancer can almost always be caught in its earliest and most curable stages by colonoscopy . Almost all men and women age 50 and older should have a colon cancer screening. Patients at risk may need screening earlier.

Colon cancer screening can find pre-cancerous polyps. Removing these polyps may prevent colon cancer.

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