Colon 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 canc
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):
It 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):
It 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):
It 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:
It 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.
Additional treatment:
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.
