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Colon Cancer
(Colorectal Cancer)
Medical Author: Dennis Lee, M.D.
Medical Reviewing Editor: Jay Marks, M.D.
• What is cancer?
• What is cancer of the colon and rectum?
• What are the causes of colon cancer?
• What are the symptoms of colon cancer?
• What tests
can be done to detect colon cancer?
• How can colon cancer be prevented?
• What are the treatments and survival for colon cancer?
• What is the follow-up care for colon cancer?
• What does the future hold for patients with colorectal
cancer?
• Colon Cancer
At A Glance
• Related colon cancer articles:
Colorectal cancer - on WebMD
What is cancer?
Cancer is a group of more than 100 different
diseases. They affect the body's basic unit, the cell. Cancer
occurs when cells become abnormal and divide without control
or order. Like all other organs of the body, the colon and
rectum are made up of many types of cells. Normally, cells
divide to produce more cells only when the body needs them.
This orderly process helps keep us healthy.
If cells keep dividing when new cells are not needed, a
mass of tissue forms. This mass of extra tissue, called
a growth or tumor, can be benign or malignant.
Benign tumors are not cancer. They can usually be removed
and, in most cases, they do not come back. Most important,
cells from benign tumors do not spread to other parts of
the body. Benign tumors are rarely a threat to life.
Malignant tumors are cancer. Cancer cells can invade and
damage tissues and organs near the tumor. Also, cancer cells
can break away from a malignant tumor and enter the bloodstream
or lymphatic system. This is how cancer spreads from the
original (primary) tumor to form new tumors in other parts
of the body. The spread of cancer is called metastasis.
When cancer spreads to another part of the body, the new
tumor has the same kind of abnormal cells and the same name
as the primary tumor. For example, if colon cancer spreads
to the liver, the cancer cells in the liver are colon cancer
cells. The disease is metastatic colon cancer (it is not
liver cancer).
What is cancer of the colon and rectum?
The colon is the part of the digestive system where
the waste material is stored. The rectum is the end of the
colon adjacent to the anus. Together, they form a long,
muscular tube called the large intestine (also known as
the large bowel). Tumors of the colon and rectum are growths
arising from the inner wall of the large intestine. Benign
tumors of the large intestine are called polyps.
Malignant tumors of the large intestine are called cancers.
Benign polyps do not invade nearby tissue or spread to other
parts of the body. Benign polyps can be easily removed during
colonoscopy, and are not life threatening. If benign polyps
are not removed from the large intestine, they can become
malignant (cancerous) over time.
Most of the cancers of the large intestine are believed
to have developed from polyps. Cancer of the colon and rectum
(also referred to as colorectal cancer) can invade and damage
adjacent tissues and organs. Cancer cells can also break
away and spread to other parts of the body (such as liver
and lung) where new tumors form. The spread of colon cancer
to distant organs is called metastasis of the colon cancer.
Once metastasis has occurred in colorectal cancer, a complete
cure of the cancer is unlikely.
Globally, cancer of the colon and rectum is the third leading
cause of cancer in males and the fourth leading cause of
cancer in females. The frequency of colorectal cancer varies
around the world. It is common in the Western world, and
is rare in Asia and Africa. In countries where the people
have adopted western diets, the incidence of colorectal
cancer is increasing.
What are the causes of colon cancer?
Doctors are certain that colorectal cancer is not contagious
(a person cannot catch the disease from a cancer patient).
Some people are more likely to develop colorectal cancer
than others. Factors that increase a person's risk of colorectal
cancer include high fat intake, a family history of colorectal
cancer and polyps, the presence of polyps in the large intestine,
and chronic ulcerative colitis.
Diet and colon cancer
Diets high in fat are believed to predispose humans to colorectal
cancer. In countries with high colorectal cancer rates,
the fat intake by the population is much higher than in
countries with low cancer rates. It is believed that the
breakdown products of fat metabolism lead to the formation
of cancer-causing chemicals (carcinogens). Diets high in
vegetables and high-fiber foods such as whole-grain breads
and cereals may rid the bowel of these carcinogens and help
reduce the risk of cancer.
Colon polyps and colon cancer
Doctors believe that most colon cancers develop in colon
polyps. Therefore, removing benign colon polyps can prevent
colorectal cancer. Colon polyps develop when chromosome
damage occurs in cells of the inner lining of the colon.
Chromosomes contain genetic information inherited from each
parent. Normally, healthy chromosomes control the growth
of cells in an orderly manner. When chromosomes are damaged,
cell growth becomes uncontrolled, resulting in masses of
extra tissue (polyps). Colon polyps are initially benign.
Over years, benign colon polyps can acquire additional chromosome
damage to become cancerous.
Ulcerative colitis and colon cancer
Chronic ulcerative colitis causes inflammation of the inner
lining of the colon. For further information, please read
the Ulcerative Colitis article. The risk of colon cancer
is much higher than average for patients with chronic ulcerative
colitis of long duration. The risk of colon cancer increases
significantly after 10 years of colitis.
Genetics and colon cancer
A person's genetic background is an important factor in
colon cancer risk. Among first-degree relatives of colon
cancer patients, the lifetime risk of developing colon cancer
is eighteen percent (a threefold increase over the general
population in the United States).
Even though family history of colon cancer is an important
risk factor, majority (80%) of colon cancers occur sporadically
in patients with no family history of colon cancer. Approximately
20% of cancers are associated with a family history of colon
cancer. And 5 % of colon cancers are due to hereditary colon
cancer syndromes. Hereditary colon caner syndromes are disorders
where affected family members have inherited cancer causing
genetic defects from one or both of the parents.
Chromosomes contain genetic information, and chromosome
damages cause genetic defects that lead to the formation
of colon polyps and later colon cancer. In sporadic polyps
and cancers (polyps and cancers that develop in the absence
of family history), the chromosome damages are acquired
(develop in a cell during adult life). The damaged chromosomes
can only be found in the polyps and the cancers that develop
from that cell. But in hereditary colon cancer syndromes,
the chromosome defects are inherited at birth and are present
in every cell in the body.
Patients who have inherited the hereditary colon cancer
syndrome genes are at risk of developing large number of
colon polyps, usually at young ages, and are at very high
risk of developing colon cancer early in life, and also
are at risk of developing cancers in other organs.
FAP (familial adenomatous polyposis) is a hereditary colon
cancer syndrome where the affected family members will develop
countless numbers (hundreds, sometimes thousands) of colon
polyps starting during the teens. Unless the condition is
detected and treated (treatment involves removal of the
colon) early, a person affected by familial polyposis syndrome
is almost sure to develop colon cancer from these polyps.
Cancers usually develop in the 40’s.
These patients are also at risk of developing other cancers
such as cancers in the thyroid gland, stomach, and the ampulla
(the part where the bile ducts drain into the duodenum just
beyond the stomach).
AFAP (attenuated familial adenomatous polyposis) is a milder
version of FAP. Affected members develop less than 100 colon
polyps. Nevertheless they are still at very high risk of
developing colon cancers at young ages. They are also at
risk of having gastric polyps and duodenal polyps.
HNPCC (hereditary nonpolyposis colon cancer) is a hereditary
colon cancer syndrome where affected family members can
develop colon polyps and cancers, usually in the right colon,
at early ages of 30’s to 40’s. Certain HNPCC patients are
also at risk of developing uterine cancer, stomach cancer,
ovarian cancer, and cancers of the ureters (the tubes that
connect the kidneys to the bladder), and the biliary tract
(the ducts that drain bile from the liver to the intestines).
MYH polyposis syndrome is a recently discovered hereditary
colon cancer syndrome. Affected members typically develop
10-100 polyps occurring at around 40 years of age, and are
at high risk of developing colon cancer.
What are the symptoms of colon cancer?
Symptoms of colon cancer are numerous
and non-specific. They include fatigue, weakness, shortness
of breath, change in bowel habits, narrow stools, diarrhea
or constipation, red or dark blood in stool, weight loss,
abdominal pain, cramps, or bloating.
Other conditions such as irritable bowel syndrome (spastic
colon), ulcerative colitis, Crohn's disease, diverticulosis,
and peptic ulcer disease can have symptoms that mimic colorectal
cancer. For more information on these conditions, please
read the following articles: Irritable Bowel Syndrome, Ulcerative
Colitis, Crohn's Disease, Diverticulosis, and Peptic Ulcer
Disease.
Colon cancer can be present for several years before symptoms
develop. Symptoms vary according to where in the large bowel
the tumor is located. The right colon is spacious, and cancers
of the right colon can grow to large sizes before they cause
any abdominal symptoms. Typically, right-sided cancers cause
iron deficiency anemia due to the slow loss of blood over
a long period of time. Iron deficiency anemia causes fatigue,
weakness, and shortness of breath. The left colon is narrower
than the right colon. Therefore, cancers of the left colon
are more likely to cause partial or complete bowel obstruction.
Cancers causing partial bowel obstruction can cause symptoms
of constipation, narrowed stool, diarrhea, abdominal pains,
cramps, and bloating. Bright red blood in the stool may
also indicate a growth near the end of the left colon or
rectum.
What tests can be done to detect colon cancer?
When colon cancer is suspected, either
a lower GI series (barium enema x-ray) or colonoscopy is
performed to confirm the diagnosis and to localize the tumor.
A barium enema involves taking x-rays of the colon and the
rectum after the patient is given an enema with a white,
chalky liquid containing barium. The barium outlines the
large intestines on the x-rays. Tumors and other abnormalities
appear as dark shadows on the x-rays. For more information,
please read the Lower Gastrointestinal Series (Barium Enema)
article.
Colonoscopy is a procedure whereby a doctor inserts a long,
flexible viewing tube into the rectum for the purpose of
inspecting the inside of the entire colon.
Colonoscopy is generally considered more accurate than barium
enema x-rays, especially in detecting small polyps. If colon
polyps are found, they are usually removed through the colonoscope
and sent to the pathologist. The pathologist examines the
polyps under the microscope to check for cancer. While the
majority of the polyps removed through the colonoscopes
are benign, many are precancerous.
Removal of precancerous polyps prevents the future development
of colon cancer from these polyps. For more information,
please read the Colonoscopy article.
If cancerous growths are found during colonoscopy, small
tissue samples (biopsies) can be obtained and examined under
the microscope to confirm the diagnosis. If colon cancer
is confirmed by a biopsy, staging examinations are performed
to determine whether the cancer has already spread to other
organs. Since colorectal cancer tends to spread to the lungs
and the liver, staging tests usually include chest x-rays,
ultrasonography, or a CAT scan of the lungs, liver, and
abdomen.
Sometimes, the doctor may obtain a blood test for CEA (carcinoembyonic
antigen). CEA is a substance produced by some cancer cells.
It is sometimes found in high levels in patients with colorectal
cancer, especially when the disease has spread.
How can colon cancer be prevented?
Unfortunately, colon cancers can be well advanced before
they are detected. The most effective prevention of colon
cancer is early detection and removal of precancerous colon
polyps before they turn cancerous. Even in cases where cancer
has already developed, early detection still significantly
improves the chances of a cure by surgically removing the
cancer before the disease spreads to other organs. Multiple
world health organizations have suggested general screening
guidelines.
Digital rectal examination and stool occult blood
testing
It is recommended that all individuals over the age of forty
have yearly digital examinations of the rectum and their
stool tested for hidden or "occult" blood. During
digital examination of the rectum, the doctor inserts a
gloved finger into the rectum to feel for abnormal growths.
Stool samples can be obtained to test for occult blood (see
below). The prostate gland can be examined at the same time.
An important screening test for colorectal cancers and polyps
is the stool occult blood test. Tumors of the colon and
rectum tend to bleed slowly into the stool. The small amount
of blood mixed into the stool is usually not visible to
the naked eye. The commonly used stool occult blood tests
rely on chemical color conversions to detect microscopic
amounts of blood.
These tests are both convenient and inexpensive. A small
amount of stool sample is smeared on a special card for
occult blood testing. Usually, three consecutive stool cards
are collected. 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
a colon cancer. Colon cancers found under these circumstances
tend to be early and have a better long term prognosis.
It is important to remember that having stool tested positive
for occult blood does not necessarily mean the person has
colon cancer. Many other conditions can cause occult blood
in the stool. However, patients with a positive stool occult
blood should undergo further evaluations involving barium
enema x-rays, colonoscopies, and other tests to exclude
colon cancer, and to explain the source of the bleeding.
It is also important to realize that stool which has tested
negative for occult blood does not mean the absence of colorectal
cancer or polyps.
Even under ideal testing conditions, at least twenty percent
of colon cancers can be missed by stool occult blood screening.
Many patients with colon polyps are tested negative for
stool occult blood. In patients suspected of having colon
tumors, and in those with high risk factors for developing
colorectal polyps and cancer, flexible sigmoidoscopies or
screening colonoscopies are performed even if the stool
occult blood tests are negative.
Flexible sigmoidoscopy and colonoscopy
Beginning at age 50, a flexible sigmoidoscopy screening
tests is recommended every 3 to 5 years.
Flexible sigmoidoscopy is an exam of the rectum and the
lower colon using a viewing tube (a short version of colonoscopy).
Recent studies have shown that the use of screening flexible
sigmoidoscopy can reduce mortality from colon cancer. This
is a result of the detection of polyps or early cancers
in people with no symptoms. If a polyp or cancer is found,
a complete colonoscopy is recommended. The majority of colon
polyps can be completely removed by colonoscopy without
open surgery. Recently doctors are recommending screening
colonoscopies instead of screening flexible sigmoidoscopies
for healthy individuals starting at ages 50-55. Please read
the Colon Cancer Screening article.
Patients with a high risk of developing colorectal cancer
may undergo colonoscopies starting at earlier ages than
50. For example, patients with family history of colon cancer
are recommended to start screening colonoscopies at an age
10 years before the earliest colon caner diagnosed in a
first degree relative, or 5 years earlier than the earliest
precancerous colon polyp discovered in a first degree relative.
Patients with hereditary colon cancer syndromes such as
FAP, AFAP, HNPCC, and MYH are recommended to begin colonoscopies
early.
The recommendations differ depending on the genetic defect,
for example in FAP; colonoscopies may begin during teenage
years to look for the development of colon polyps. Patients
with a prior history of polyps or colon cancer may also
undergo colonoscopies to exclude recurrence. Patients with
a long history (greater than 10 years) of chronic ulcerative
colitis have an increased risk of colon cancer, and should
have regular colonoscopies to look for precancerous changes
in the colon lining.
Genetic counseling and testing
Blood tests are now available to test for FAP, AFAP, MYH,
and HNPCC hereditary colon cancer syndromes.
Families with multiple members having colon cancers, members
with multiple colon polyps, members having cancers at young
ages, and having other cancers such as cancers of the ureters,
uterus, duodenum, etc. should be referred for genetic counseling
followed possibly by genetic testing. Genetic testing without
prior counseling is discouraged because of the extensive
family education that is involved and the complicated nature
of interpreting the test results.
The advantages of genetic counseling followed by genetic
testing include:
1) identifying family members at high risk of developing
colon cancer to begin colonoscopies early,
2) identifying high risk members so that screening may begin
to prevent other cancers such as ultrasound tests for uterine
cancer, urine examinations for ureter cancer, and upper
endoscopies for stomach and duodenal cancers,
3) alleviating concern for members who test negative for
the hereditary genetic defects.
Diet and colon cancer to prevent colon cancer
People can change their eating habits by reducing fat intake,
and increasing fiber (roughage) in their diet.
Major sources of fat are meat, eggs, dairy products, salad
dressings, and oils used in cooking. Fiber is the insoluble,
non- digestible part of plant material present in fruits,
vegetables, and whole-grain breads and cereals. It is postulated
that high fiber in the diet leads to the creation of bulky
stools which can rid the intestines of potential carcinogens.
In addition, fiber leads to the more rapid transit of fecal
material through the intestine, thus allowing less time
for a potential carcinogen to react with the intestinal
lining.
For additional information, please read the Colon Cancer
Prevention article.
What are the treatments and survival for colon cancer?
Surgery is the most common treatment for colorectal
cancer. During surgery, the tumor, a small margin of the
surrounding healthy bowel, and adjacent lymph nodes are
removed. The surgeon then reconnects the healthy sections
of the bowel. In patients with rectal cancer, the rectum
is permanently removed. The surgeon then creates an opening
(colostomy) on the abdomen wall through which solid waste
in the colon is excreted. Specially trained nurses (enterostomal
therapists) can help patients adjust to colostomies, and
most patients with colostomies return to a normal lifestyle.
The long term prognosis after surgery depends on whether
the cancer has spread to other organs (metastasis). The
risk of metastasis is proportional to the depth of penetration
of the cancer into the bowel wall. In patients with early
colon cancer which is limited to the superficial layer of
the bowel wall, surgery is often the only treatment needed.
These patients can experience long term survival in excess
of eighty percent. In patients with advanced colon cancer,
wherein the tumor has penetrated beyond the bowel wall and
there is evidence of metastasis to distant organs, the five
year survival rate is less than ten percent.
In some patients, there is no evidence of distant metastasis
at the time of surgery, but the cancer has penetrated deeply
into the colon wall, or reached adjacent lymph nodes. These
patients are at risk of tumor recurrence either locally
or in distant organs. Chemotherapy in these patients may
delay tumor recurrence and improve survival.
Chemotherapy is the use of medications to kill cancer cells.
It is a systemic therapy, meaning that the medication travels
throughout the body to destroy cancer cells. After colon
cancer surgery, some patients may harbor microscopic metastasis
(small foci of cancer cells that cannot be detected).
Chemotherapy is given shortly after surgery to destroy these
microscopic cells. Chemotherapy given in this manner is
called adjuvant chemotherapy.
Recent studies have shown increased survival and delay of
tumor recurrence in some patients treated with adjuvant
chemotherapy within five weeks of surgery. Most drug regimens
have included the use of 5-flourauracil (5-FU). On the other
hand, chemotherapy for shrinking or controlling the growth
of metastatic tumors has been disappointing. Improvement
in the overall survival for patients with widespread metastasis
has not been convincingly demonstrated.
Chemotherapy is usually given in a doctor's office, in the
hospital as a outpatient, or at home.
Chemotherapy is usually given in cycles of treatment periods
followed by recovery periods. Side effects of chemotherapy
vary from person to person, and also depend on the agents
given. Modern chemotherapy agents are usually well tolerated,
and side effects are manageable. In general, anticancer
medications destroy cells that are rapidly growing and dividing.
Therefore, red blood cells, platelets, and white blood cells
are frequently affected by chemotherapy.
Common side effects include anemia, loss of energy, easy
bruising, and a low resistance to infections. Cells in the
hair roots and intestines also divide rapidly. Therefore,
chemotherapy can cause hair loss, mouth sores, nausea, vomiting,
and diarrhea.
Radiation therapy in colorectal cancer has been limited
to treating cancer of the rectum. There is a decreased local
recurrence of rectal cancer in patients receiving radiation
either prior to or after surgery.
Without radiation, the risk of rectal cancer recurrence
is close to fifty percent. With radiation, the risk is lowered
to approximately seven percent. Side effects of radiation
treatment include fatigue, temporary or permanent pelvic
hair loss, and skin irritation in the treated areas.
Other treatments have included the use of localized infusion
of chemotherapeutic agents into the liver, the most common
site of metastasis. This involves the insertion of a pump
into the blood supply of the liver which can deliver high
doses of medicine directly to the liver tumor. Response
rates for these treatments have been reported to be as high
as eighty percent.
Side effects, however, can be serious. Additional experimental
agents considered for the treatment of colon cancer include
the use of cancer-seeking antibodies bound to cancer fighting
drugs. Such combinations can specifically seek and destroy
tumor tissues in the body. Other treatments attempt to boost
the immune system, the bodies' own defense system, in an
effort to more effectively attack and control colon cancer.
In patients who are poor surgical risks, but who have large
tumors which are causing obstruction or bleeding, laser
treatment can be used to destroy cancerous tissue and relieve
associated symptoms. Still other experimental agents include
the use of photodynamic therapy. In this treatment, a light
sensitive agent is taken up by the tumor which can then
be activated to cause tumor destruction.
What is the follow-up care for colon cancer?
Follow-up exams are important after treatment for
colon cancer. The cancer can recur near the original site
or in a distant organ such as the liver or lung.
Follow-up exams include a physical examination by the doctor,
blood tests of liver enzymes, chest x-rays, CAT scans of
the abdomen and pelvis, colonoscopies, and blood CEA levels.
Abnormal liver enzymes may indicate growth of liver metastasis.
CEA levels may be elevated before surgery, and become normal
shortly after the cancer is removed. Slowly rising CEA level
may indicate cancer recurrence. A CAT scan of the abdomen
and pelvis can show tumor recurrence in the liver, pelvis,
or other areas. Colonoscopy can show recurrence of polyps
or cancer in the large intestine.
In addition to checking for cancer recurrence, patients
who have had colon cancer may have an increased risk of
cancer of the prostate, breast, and ovary. Therefore, follow-up
examinations should include these areas.
What does the future hold for patients with colorectal
cancer?
Colon cancer remains a major cause of death and
disease, especially in the Western world. A clear understanding
of the causes and course of the disease is emerging. This
has allowed for recommendations regarding screening for
and prevention of this disease. The removal of colon polyps
helps prevent colon cancer. Early detection of colon cancer
can improve the chances of a cure and overall survival.
Treatment remains unsatisfactory for advanced disease, but
research in this area remains strong and newer treatments
continue to emerge.
New and exciting preventive measures have recently focused
on the possible beneficial effects of aspirin or other anti-inflammatory
agents. In trials, the use of these agents has markedly
limited colon cancer formation in several experimental models.
Other agents being evaluated to prevent colon cancer include
calcium, selenium, and vitamins A, C, and E.
More studies are needed before these agents can be recommended
for widespread use by the public to prevent colon cancer.
Colon Cancer At A Glance
• Colorectal cancer is a malignant tumor arising from the
inner wall of the large intestine.
• Colorectal cancer is the third leading cause of cancer
in males, fourth in females in the U.S.
• Risk factors for colorectal cancer include heredity, colon
polyps, and long standing ulcerative colitis.
• Most colorectal cancers develop from polyps. Removal of
colon polyps can prevent colorectal cancer.
• Colon polyps and early cancer can have no symptoms. Therefore
regular screening is important.
• Diagnosis of colorectal cancer can be made by barium enema
or by colonoscopy with biopsy confirmation of cancer tissue.
• Treatment of colorectal cancer depends on the location,
size, and extent of cancer spread, as well as the age and
health of the patient.
• Surgery is the most common treatment for colorectal cancer.
http://www.medicinenet.com/
colon_cancer/article.htm
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