Colon cancer Definition
Colon cancer is cancer of the large intestine (colon),
the lower part of your digestive system. Rectal cancer is cancer of the last 6
inches of the colon. Together, they're often referred to as colorectal cancers.
About 112,000 people are diagnosed with colon cancer annually, and about 41,000
new cases of rectal cancer are diagnosed each year, according to the American
Most cases of colon cancer begin as small, non-cancerous (benign) clumps of
cells called adenomatous polyps. Over time some of these polyps become colon
Polyps may be small and produce few, if any, symptoms. Regular screening tests
can help prevent colon cancer by identifying polyps before they become
cancerous. If signs and symptoms of colon cancer do appear, they may include
changes in bowel habits, blood in your stool, persistent cramping, gas or
Many people with colon cancer experience no symptoms in
the early stages of the disease. When symptoms appear, they'll likely vary,
depending on the cancer's size and location in your large intestine.
Signs and symptoms of colon cancer include:
A change in your bowel habits, including diarrhea or
constipation or a change in the consistency of your stool for more than a couple
Rectal bleeding or blood in your stool
Persistent abdominal discomfort, such as cramps, gas or pain
Abdominal pain with a bowel movement
A feeling that your bowel doesn't empty completely
Weakness or fatigue
Unexplained weight loss
Blood in your stool may be a sign of cancer, but it can also indicate other
conditions. Bright red blood you notice on bathroom tissue more commonly comes
from hemorrhoids or minor tears (fissures) in your anus, for example. In
addition, certain foods, such as beets or red licorice, can turn your stools
red. Iron supplements and some anti-diarrheal medications may make stools black.
Still, it's best to have any sign of blood or change in your stools checked
promptly by your doctor because it can be a sign of something more serious.
In general, cancer occurs when healthy cells become
altered. Healthy cells grow and divide in an orderly way to keep your body
functioning normally. But sometimes this growth gets out of control — cells
continue dividing even when new cells aren't needed. In the colon and rectum,
this exaggerated growth may cause precancerous cells to form in the lining of
your intestine. Over a long period of time — spanning up to several years — some
of these areas of abnormal cells may become cancerous. In later stages of the
disease, colon cancer may penetrate the colon walls and spread (metastasize) to
nearby lymph nodes or other organs. As with most cancers, the exact cause for
colon cancer is unknown.
Precancerous growths in the colon
Precancerous cells can occur anywhere in your large intestine, the muscular tube
that forms the last part of your gastrointestinal tract. The colon comprises the
upper 4 to 5 feet of your large intestine, and the rectum makes up the lower 6
Precancerous growths most commonly occur as clumps of cells (polyps) that extend
from the wall of the colon. Polyps can appear mushroom-shaped. Precancerous
growths can also be flat or recessed into the wall of the colon (nonpolypoid
lesions). Nonpolypoid lesions are more difficult to detect, but are less common.
Several types of colon polyps exist. Among the most common are:
Adenomas. These polyps have the potential to become cancerous and are usually
removed during screening tests such as flexible sigmoidoscopy or colonoscopy.
Hyperplastic polyps. These polyps are rarely, if ever, a risk factor for
Inflammatory polyps. These polyps may follow a bout of ulcerative colitis. Some
inflammatory polyps may become cancerous, so having ulcerative colitis increases
your overall risk of colon cancer.
Factors that may increase your risk of colon cancer
Age. About 90 percent of people diagnosed with colon cancer are older than 50.
Colon cancer can occur in younger people, but it occurs much less frequently.
A personal history of colorectal cancer or polyps. If you've already had colon
cancer or adenomatous polyps, you have a greater risk of colon cancer in the
Inflammatory intestinal conditions. Long-standing inflammatory diseases of the
colon, such as ulcerative colitis and Crohn's disease, can increase your risk of
Inherited disorders that affect the colon. Genetic syndromes passed through
generations of your family can increase your risk of colon cancer. These
syndromes cause only about 5 percent of all colon cancers. One genetic syndrome
called familial adenomatous polyposis (FAP) is a rare disorder that causes you
to develop thousands of polyps in the lining of your colon and rectum. People
with untreated FAP have a greater than 90 percent chance of developing colon
cancer by age 45. Another genetic syndrome, hereditary nonpolyposis colorectal
cancer (HNPCC), also called Lynch syndrome, is more common than FAP. People with
HNPCC have an increased risk of colon cancer and tend to develop colon cancer at
an early age. Both FAP and HNPCC can be detected through genetic testing. Talk
to your doctor about whether your family history suggests you have a risk of
Family history of colon cancer and colon polyps. You're more likely to develop
colon cancer if you have a parent, sibling or child with the disease. If more
than one family member has colon cancer or rectal cancer, your risk is even
greater. In some cases, this connection may not be hereditary or genetic.
Instead, cancers within the same family may result from shared exposure to an
environmental carcinogen or from diet or lifestyle factors.
Diet. Colon cancer and rectal cancer may be associated with a diet low in fiber
and high in fat and calories. Research in this area has had mixed results. Some
studies have found an increased risk of colon cancer in people who eat diets
high in red meat and processed meats.
People who eat a diet similar to that of Western
countries, such as the United States and Europe, have a higher risk of
developing colon cancer than do people who eat diets typically seen in
developing countries. When people move from a developing country to a Western
country and adapt to the Western diet, their risk of colon cancer increases.
Although many studies have tried to identify what part of the Western diet may
cause colon cancer, the answer remains unknown.
A sedentary lifestyle. If you're inactive, you're more likely to develop colon
cancer. This may be because when you're inactive, waste stays in your colon
longer. Getting regular physical activity may reduce your risk.
Diabetes. People with diabetes and insulin resistance may have an increased risk
of colon cancer.
Obesity. People who are obese have an increased risk of colon cancer and an
increased risk of dying of colon cancer when compared with people considered
Smoking. People who smoke cigarettes may have an increased risk of colon cancer.
They may also have an increased chance of dying of colon cancer.
Alcohol. Heavy use of alcohol may increase your odds of colon cancer.
Growth hormone disorder. Acromegaly, an uncommon disorder that causes an excess
of growth hormone in your body, may increase your risk of colon polyps and colon
Radiation therapy for cancer. Radiation therapy directed at the abdomen to treat
previous cancers may increase the risk of colon cancer.
When to seek medical advice
If you notice any symptoms of colon cancer, such as blood in your stool or a
persistent change in bowel habits, see your doctor as soon as possible. Keep in
mind that colorectal cancer can occur in younger as well as older people. If
you're at high risk, don't wait until symptoms appear. See your doctor for
Talk to your doctor about when you should begin screening for colon cancer.
Guidelines generally recommend colon cancer screenings begin at age 50. Your
doctor may recommend more frequent or earlier screening if you have other risk
factors, such as a family history of the disease.
Tests and diagnosis
Most colon cancers develop from adenomatous polyps. Screening can detect polyps
before they become cancerous. Screening may also detect colon cancer in its
early stages when there is a good chance for cure.
You may be embarrassed by the screening procedures,
worried about discomfort or afraid of the results. Discuss your screening
options and your concerns with your doctor. Most procedures are only moderately
uncomfortable, and working with a doctor you like and trust can help ease your
Common screening and diagnostic procedures
include the following:
Stool blood test. The fecal occult (hidden) blood test
checks a sample of your stool for blood. It can be performed in your doctor's
office, but you're usually given a kit that explains how to take the sample at
home. You return the sample to a lab or your doctor's office to be checked. Not
all cancers can be detected with a stool blood test, since not all cancers bleed
and those that do often bleed intermittently. This can result in a negative test
result, even though you may have cancer. If blood is detected in your stool,
your doctor may order other screening tests to determine the source of the
blood. Blood in your stool can be the result of hemorrhoids or an intestinal
condition other than cancer. Certain foods also may alter test results,
suggesting blood in the colon when there is none.
Flexible sigmoidoscopy. In this test, your doctor uses a flexible, slender and
lighted tube to examine your rectum and sigmoid — approximately the last 2 feet
of your colon. The test usually takes just a few minutes. It can sometimes be
uncomfortable, and there's a slight risk of perforating the colon wall. If a
polyp or colon cancer is found during this exam, your doctor will recommend
colonoscopy to look at the entire colon and remove any polyps that are present
for examination under a microscope. Because sigmoidoscopy only examines the
lower third of the colon, polyps or cancer in the rest of the colon won't be
Barium enema. This diagnostic test allows your doctor to evaluate your entire
large intestine with an X-ray. Barium, a contrast dye, is placed into your bowel
in an enema form. During a double-contrast barium enema, air is also added. The
barium fills and coats the lining of the bowel, creating a clear silhouette of
your rectum, colon and sometimes a small portion of your small intestine.
There's also a slight risk of perforating the colon wall, and the test has a
significantly high rate of missing important lesions. A flexible sigmoidoscopy
is often done in addition to the barium enema to aid in detecting small polyps
that a barium enema X-ray may miss, especially in the lower bowel and rectum.
Barium enema may miss small polyps or small cancers. If an abnormality is
detected using barium enema, your doctor may recommend a colonoscopy.
Colonoscopy. Colonoscopy is similar to flexible sigmoidoscopy, but the
instrument used — a colonoscope, which is a long, flexible and slender tube
attached to a video camera and monitor — allows your doctor to view your entire
colon and rectum. If any polyps are found during the exam, your doctor may
remove them immediately or take tissue samples (biopsies) for analysis. This is
done through the colonoscope and is painless.
You may receive a mild sedative to make you more comfortable. Preparation for
the procedure involves drinking a large amount of fluid containing a laxative to
clean out your colon — enemas are no longer necessary. Major risks of diagnostic
colonoscopy include bleeding and perforation of the colon wall, but these are
Virtual colonoscopy (CT colonography). Though not available at all medical
centers, virtual colonoscopy may be one screening option. Virtual colonoscopy
uses a computerized tomography (CT) machine to take images of your colon, rather
than using a scope inserted in your rectum to see inside your colon. Virtual
colonoscopy still requires that you undergo a bowel preparation to remove any
stool. If any abnormalities are detected on virtual colonoscopy, you'll still
need to undergo conventional colonoscopy. Research into virtual colonoscopy is