University Pathologists - Resource Center
RESOURCE ARCHIVE > COLONIC ADENOCARCINOMA
provided by Mirela Stancu, MD
Colorectal adenocarcinoma is a malignant (cancerous) growth of the cells lining the
internal surface of the large intestine (colon) and rectum. Most colorectal
adenocarcinomas develop after many years in benign cell growths called adenomatous polyps
(see
tutorial). Thus, the complete removal of the polyps during colonoscopy effectively
prevents the development of cancer.
Colorectal carcinoma is one of the few preventable malignancies and is the
second-leading cause of cancer-related deaths in the United States after the lung cancer.
Both men and women of older age are equally affected. Afrin Americans have a higher cancer
incidence and mortality rate.
The incidence of colorectal carcinoma has steadily decreased since 1980s due to the
introduction of screening colonoscopy. It is estimated that 135,000 people develop
colorectal carcinoma yearly.
The causes of colorectal carcinoma are multifactorial and include genetic, chronic
inflammatory diseases of the intestine and environmental factors.
Most of the colorectal carcinomas are sporadic (are not part of a known inherited cancer
syndrome), but even those have a tendency to run in the families. People with personal
history of adenomatous polyps or carcinoma, and first-degree relatives of patients with
polyps or carcinoma detected at an age younger than 60 years, are at increased risk.
Approximately 5% of the cases of colorectal carcinomas belong to certain inherited cancer
syndromes (Familial Adenomatous Polyposis, Gardner syndrome, Lynch syndrome). These cases
arise due to well-studied genetic mutations that are passed on to some family members.
Thus, it is important to examine and provide genetic consultation to all members of
families with inherited cancer syndromes.
Similar to adenomatous polyps of colon and rectum, environmental risk factors for
colorectal carcinoma, include older age, high fat and red meat diet, low fiber intake,
tobacco and obesity. Other causes for colorectal malignancies include chronic inflammatory
bowel diseases such as ulcerative colitis (see
tutorial) and Crohn's disease (see
tutorial).
In approximately 70% of the patients none of the above risk factors can be detected.
People with early colorectal adenocarcinoma do not usually have any symptoms or signs.
When the cancer has an accelerated growth rate, it may ulcerate and bleed. Thus the most
common sign of locally advanced colorectal carcinomas is rectal bleeding (red blood
streaks on the stool) or melena (black stools caused by digested blood). If the bleeding
is continuous and severe, the patient may develop iron deficient anemia. Other symptoms
occurring with advanced cancers include loss of appetite, weight loss, abdominal pain and,
in the case of bowel obstruction (blockage) by a large tumor, abdominal distention,
constipation, pain, nausea and vomiting.
The colorectal cancer is usually detected during screening colonoscopy, follow-up
endoscopy for prior personal history of polyps or cancer, and during diagnostic work-up
for iron deficient anemia or rectal bleeding.
Common diagnostic and/or screening procedures for colorectal carcinoma include:
· Digital rectal examination. This procedure takes place in the
physician's office and consists of direct examination of the lower few inches of the
rectum using a gloved finger. The doctor can detect both rectal carcinomas and larger
polyps located in the lower portion of the rectum.
· Fecal occult blood test. This test detects traces of blood in a stool
sample by using a chemical reaction. This test is not very specific , since conditions
other than colorectal cancer can present with blood in stool (internal hemorrhoids, benign
polyps, vascular lesions, solitary colonic or rectal ulcers). On the other hand, negative
fecal occult blood test cannot exclude the possibility of a cancer, since not all cancers
bleed. Therefore, other screening tests or procedures are recommended in addition to FOBT.
If the test detects blood breakdown products in the stool, a colonoscopy or flexible
sigmoidoscopy is recommended.
· Flexible sigmoidoscopy. This procedure is used by physicians to
directly visualize the internal lining of the lower portion of the colon, sigmoid colon
and rectum. Approximately half of all colonic cancers occur in this portion of colon.
During this procedure a thin tube equipped with a tiny video camera is passed into the
rectum and advanced into sigmoid colon. The images captured by the video camera are
transferred to a video monitor and examined by the doctor. At the same time, if a
suspicious lesion is identified, small samples of the lesion (biopsies) can be taken using
small forceps. Colorectal carcinoma appears as an irregular growth of tissue bulging into
the colon's passageway called lumen. Because this procedure can be used to examine only
the rectum and the left part of the colon, the tumors located in the right and transverse
colon will be missed. Therefore, a different procedure is commonly used.
· Colonoscopy. Colonoscopy is, in principle, similar to the flexible
sigmoidoscopy, allowing to visually examine the entire colon by using a thin, long,
flexible tube called colonoscope. The procedure takes place under mild sedation and lasts
about 30 minutes. One day prior to the procedure the colon must be prepared by drinking a
large amount of laxative. If the colon is not completely clean the colonoscopy may miss
important lesions. The complications associated with colonoscopy are uncommon and may
include bleeding and perforation.
· Barium enema. This procedure is usually performed in conjunction with
flexible sigmoidoscopy. During the procedure a contrast substance (barium) is passed into
the rectum and colon by using an enema. The barium fills and lines the entire colonic
mucosa, producing a clear image on X-ray. Complications are rare and include perforation.
Colorectal carcinoma develops over many years from adenomatous polyps. Initially, the
cancer is confined to the inner layer of the colonic or rectal wall called mucosa. Once it
accumulates numerous genetic abnormalities, the cancer spreads locally, invading
successively into the outer layers of the bowel wall (submucosa, muscularis and serosa).
It can also spread to the local lymph nodes (lymph node metastases) or to distant organs
(distant metastases). Each of these stages are associated with a different survival rate
at 5 years after treatment, which is high (close to 90%) for early carcinomas and low
(approximately 40-50%) for metastatic carcinomas (carcinoma that already spread).
The stages of colonic adenocarcinomas are based on the extent of the cancerous cells and
are defined as follows:
Stage 0 - The cancer is confined to the inner lining of the colon (mucosa).
Stage I - The cancer has invaded beyond the mucosa, but it is confined to the colonic
wall.
Stage II - The cancer spread beyond the colonic wall but not to the regional lymph nodes.
Stage III - The cancer has spread to the local lymph nodes but not to the other organs.
Stage IV - The cancer has spread to distant organs (metastatic tumor).
Complications of locally advanced cancer include intestinal obstruction (constipation,
abdominal distention, nausea, vomiting, loss of appetite), perforation (abdominal pain),
extreme weight loss, anemia, creation of passages (fistulas) between colon/rectum and
nearby organs (bladder, internal genital organs) with passing of gas, fecaloid material or
necrotic debris into urine.
The treatment options for colorectal carcinoma depend on the stage of the disease, and
include: surgery, chemotherapy and radiation therapy.
Surgery is the primary treatment for colorectal carcinoma and consists of removal of the
segment of colon containing the cancer (colectomy). Depending on the location of the
cancer, a portion of the lower end of the small intestine will be removed together with
the segment of the colon (for right-sided tumors) or a colostomy may be necessary for low
rectal tumors. A colostomy is an opening in the abdominal wall to which a portion of the
bowel is sutured, allowing for the evacuation of the fecal material into a pouch taped to
the abdominal wall. The colostomies can be temporary or permanent. The recovery from
surgery has a few side-effects including pain, diarrhea or constipation. When the cancer
is small, it may be removed by laparoscopic surgery, which has a shortened recovery and
fewer side effects compared with the conventional surgery. If the tumor is locally
advanced but didn't spread to distant organs, the physicians may recommend chemotherapy
and/or radiation therapy before the surgery. This approach may help shrink the tumor and
make it easier to resect.
After surgery, the colon with neighboring tissue containing lymph nodes is sent to the
pathology lab for microscopic examination and pathologic diagnosis. If metastases are
detected in the regional lymph nodes, chemotherapy is recommended. Chemotherapy uses
potent drugs that destroy the cancer cells that may circulate in the blood or lymphatic
stream. The chemotherapy drugs will indiscriminately affect some of the benign tissues
with rapid growth rate. Thus, the side effects include nausea, vomiting, fatigue, hair
loss, diarrhea, mouth ulcers and infections.
Radiation therapy is used either before surgery to shrink the large rectal tumors or after
surgery to destroy tumor cells that can be left behind. It can be used in conjunction with
the chemotherapy, and consists of targeting the tumor with X-rays in much higher dose than
that usually used for diagnostic purposes. The therapeutic X-rays will only kill the
tumor, sparing the normal tissues around it. The side effects of the radiotherapy include
diarrhea, rectal bleeding, nausea, fatigue and minor local skin irritation.
The role of diet is important in reducing the risk of colorectal carcinoma and adenomatous
polyps. Increasing the amount of fruit, vegetables and whole grains, reducing the intake
of animal fat, and getting the adequate amount of calcium daily are beneficial. Lifestyle
adjustments, such as quitting smoking, reducing the amount of daily alcohol and reducing
the body weight by daily exercise, are important steps in reducing the risk of colorectal
carcinoma even for individuals with strong family history.
Mayo Clinic
National Cancer Institute
Cleveland Clinic Foundation
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