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Colorectal cancer is a disease in which malignant (cancer) cells form in the tissues of the colon or rectum.
It is the third most common cancer and the third leading cause of cancer-related
death in the United States. Over the past decade, colorectal cancer incidence
and mortality rates have modestly decreased or remained level.
The colon is the first 6 feet of the large intestine in the digestive system. The last 6 inches are the rectum and the anal canal. The anal canal ends at the anus (the opening of the large intestine to the outside of the body).
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Symptoms
The following symptoms may be caused by colorectal cancer. Other conditions may cause the same symptoms.
- A change in bowel habits.
- Blood (either bright red or very dark) in the stool.
- Diarrhea, constipation, or feeling that the bowel does not empty completely.
- Stools that are narrower than usual.
- Frequent gas pains, bloating, fullness, or cramps.
- Weight loss for no known reason.
- Feeling very tired.
- Vomiting.
Diagnosis
The following tests and procedures may be used:
- Physical exam and history: An exam of the body to check general signs of
health.
- Fecal occult blood test: A test to check stool (solid waste) for blood that can only be seen with a microscope.
- Digital rectal exam: An exam of the rectum. The doctor or nurse inserts a lubricated, gloved finger into the rectum to feel for lumps or anything else that seems unusual.
- Biopsy: The removal of cells or tissues so they can be viewed under a microscope to check for signs of cancer.
- Barium enema.
- Sigmoidoscopy.
- Colonoscopy.
- Virtual colonoscopy.
Causes
All cancers are caused by dysfunctions of proteins involved in cell division, apoptosis, or DNA repair (see general characteristics). Dysfunctional proteins may arise from gene mutations or protein interactions with environments. A tumor suppressor gene, APC, and several DNA repair genes, MSH2, MSH6 and MLH1, are known to be associated with colorectal cancer
(more info). The following risk
factors may increase the chance of developing colorectal cancer:
- A diet high in fat.
- Cigarette smoking.
- Drinking alcohol.
- Obesity.
Reference:
National Cancer Institute, USA.
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