Colon cancer, commonly grouped together with colorectal cancer,
is cancer of the large intestine – the final portion of the digestive tract. It is the
most common of all gastrointestinal cancers. Colon cancer usually starts from a small growth
called a polyp. Polyps are very common, but most polyps do NOT become cancers. Polyps can be of
various types, some of which are more likely to develop into malignant tumors than others.
Early-stage colon cancer generally produces NO symptoms. Advanced-stage symptoms vary depending
on the location of the tumor, and may include: changes in bowel habits that persist for weeks;
blood in stool; abdominal pain and discomfort; constant feeling that the bowel doesn't empty
completely; fatigue; and unexplained weight loss. Early detection is the key to prevent colon
cancer. Because a precancerous polyp usually takes years to develop into a malignant tumor,
colon cancer can be effectively prevented with regular screening.
There are 2 major types of screening tests: - Stool-based tests: stool samples are examined
for signs of cancer, such as blood and mutated DNA. These tests are non-invasive but less
effective and need to be done more often. - Visual screening, such as colonoscopy,
is more reliable and can be done every 5 or 10 years. Colonoscopy uses a long, flexible tube
equipped with a camera and light, to view the entire colon. If polyps or abnormal structures
are found, surgical tools are passed through the tube to remove polyps or take tissue samples for
analysis. Typically, any polyps found in the colon are removed during colonoscopy and examined for
pre-cancerous changes, known as dysplasia. If high-grade dysplasia is detected, a follow-up
colonoscopy is required to monitor the condition. Colorectal cancers are caused by mutations that
increase the rate of cellular division. Some of these mutations can be inherited from parents.
Examples of inherited colorectal cancers include: - Familial adenomatous polyposis, or FAP:
a condition caused by mutations in the APC gene. The APC protein acts as a tumor suppressor,
keeping cells from growing and dividing too fast. Mutations in APC result in
uncontrolled cell division, causing hundreds of polyps to grow in the colon. FAP patients
usually develop colon cancer by the age of 40. - Lynch syndrome: another inherited condition
caused by changes in genes that normally help repair DNA damages. A faulty DNA repair
results in increased rate of mutations. Patients are at high risks of colorectal
cancer as well as other types of cancers. In most cases, however, the mutations that
lead to cancer are acquired during a person’s life rather than being inherited. The early
event is usually a mutation in the same APC gene that is responsible for FAP. While
FAP is a rare condition, APC mutations are very common in sporadic colorectal cancers.
Apart from genetic predisposition, other risks factors for colon cancer include:
aging, high-red meat and low-fiber diets, obesity, alcohol use, smoking, diabetes,
and inflammatory intestinal conditions, such as ulcerative colitis and Crohn's disease.