Colorectal cancer
(Colon Cancer) includes cancerous
growths in the colon, rectum and appendix.
It is the third most common form of cancer
and the second leading cause of death among cancers in the Western world. Many colorectal cancers (Colon Cancers) are thought to arise from
polyps in the colon. These mushroom-like
growths are usually benign, but some may
develop into colon cancer over time. Diagnosis is
by colonoscopy. Therapy is usually through
surgery, with many cases also requiring
chemotherapy.
Colon Cancer Symptoms
Colon Cancer
early Symptoms include:
- Change in bowel habits.
- Blood in stools (melena, hematochezia).
- Bowel obstruction (rare) by the tumor
Often, these symptoms (which can be associated
with colon cancer) are much less specific:
- Unexplained
weight loss.
-
Anemia, with symptoms such as tiredness,
malaise, pallor
- Hepatomegaly (enlargement of the liver) due to
speading of the tumor
It is also possible that there will be no
symptoms of Colon Cancers at all. This is one reason why some
recommend periodical screening for the disease.
Risk Factors of Colon Cancer
The lifetime risk of developing
colon cancer in
the United States is about 7%. Certain factors
increase a person's risk of developing colon
cancer.
These include:
- Age. The risk of developing
colorectal cancer (colon cancer)
increases with age.
Most cases occur in the 60s
and 70s, while cases before age 50 are uncommon
unless a family history of early colon cancer is
present.
- History of
cancer. Women who have had
cancer
of the breast, uterus, or ovary are at higher risk
of developing colorectal cancer.
- Heredity:
- Family history of
colon cancer, especially in
a close relative before the age of 55 or multiple
relatives
-
Familial adenomatous polyposis (FAP) carries a
near 100% risk of developing colorectal cancer by
the age of 40 if untreated
- Hereditary nonpolyposis
colorectal cancer (HNPCC)
or Lynch syndrome
- Long-standing ulcerative colitis or
Crohn's
disease of the colon, approximately 30% after 25
years if the entire colon is involved
- Smoking.
Smokers are more likely to die of
colon cancer than non-smokers
- Diet. Some studies have shown that people who
have diets high in fresh fruit, vegetables,
poultry and fish and low in red meat are at
reduced risk of colorectal cancer (Colon
Cancer).
- Physical inactivity. People who are physically
active are at lower risk of developing colorectal
cancer (colon cancer).
- Virus. Exposure to some viruses (such as human
papilloma virus) may be associated with colorectal
cancer (Colon Cancer).
Diagnosis, Screening and Monitoring of Colon Cancer
Indentification of malignancy
Colorectal cancer (Colon Cancer) can take many years to develop and
early detection of colorectal cancer greatly
improves the chances of a cure. Therefore, screening
for the colon cancers is recommended in individuals who
are at increased risk. There are several different
tests available for this purpose.
- Digital rectal exam (DRE): The doctor inserts
a lubricated, gloved finger into the rectum to
feel for abnormal areas.
It only detects tumors
large enough to be felt in the distal part of the
rectum and is not really a screening test.
- Fecal occult blood test (FOBT): a test for
blood in the stool.
- Endoscopy:
- Sigmoidoscopy: A lighted probe (sigmoidoscope)
is inserted into the rectum and lower colon to
check for polyps and other abnormalities.
-
Colonoscopy: A lighted probe called a
colonoscope is inserted into the rectum and the
entire colon to look for polyps and other
abnormalities that may be caused by colon cancer.
A
colonoscopy has the advantage that if polyps are
found during the procedure they can be immediately
removed. Tissue can also be taken for biopsy.
- Double contrast barium enema (DCBE): First, an
overnight preparation is taken to cleanse the
colon. An enema containing barium sulfate is
administered, then air is insufflated into the
colon, distending it. The result is a thin layer
of barium over the inner lining of the colon which
is visible on X-ray films. A colon cancer or a
precancerous polyp can be detected this way. This
technique can miss the (less common) flat polyp.
- Virtual colonoscopy replaces X-ray films in
the double contrast barium enema (above) with a
special computed tomography scan and requires
special workstation software in order for the
radiologist to interpret. This technique is
approaching colonoscopy in sensitivity for polyps.
However, any
polyps found must still be removed by
standard colonoscopy.
- Standard computed axial tomography is an x-ray
method that can be used to determine the degree of
spread of colon cancer, but is not sensitive enough to
use for screening. Some
cancers are found in CAT
scans performed for other reasons.
- Blood tests: Measurement of the patient's
blood for elevated levels of certain proteins can
give an indication of tumor load. In particular,
high levels of carcinoembryonic antigen CEA in the
blood can indicate metastasis of adenocarcinoma.
These tests are frequently false positive or false
negative, and are not recommended for screening.
- Genetic counseling and genetic testing for
families who may have a heriditary form of colon
cancer, such as Hereditary nonpolyposis colorectal
cancer (HNPCC) or Familial adenomatous polyposis (FAP).
- Positron emission tomography (PET) is a
3-dimensional scanning technology where a
radioactive sugar is injected into the patient,
the sugar collects in tissues with high metabolic
activity, and an image is formed by measuring the
emission of radiation from the sugar. Because
cancer cells often have very high metabolic rate,
this can be used to differentiate benign and
malignant tumors. PET is not used for screening
and does not (yet) have a place in routine workup
of colorectal cancer cases.
Pathology of
Colon Cancer
The pathology of the tumor / colon
cancer is usually reported
from the analysis of tissue taken from a biopsy or
surgery. A pathology report will usually contain a
description of cell type and grade.
The most common
colon cancer cell type is adenocarcinoma which
accounts for 95% of cases. Other, rarer types
include
lymphoma and squamous cell carcinoma.
Cancers on the right side (ascending colon and
caecum) tend to be exophytic, that is the tumour
grows outwards from one location in the bowel wall.
This very rarely causes obstruction of feces, and
present with symptoms such as
anemia. Left-sided tumours tend to be circumferential, and can obstruct
the bowel much like a napkin ring.
Histopathology: Adenocarcinoma is a malignant
epithelial tumor, originating from glandular
epithelium of the colorectal mucosa. It invades the
wall, infiltrating the muscularis mucosae, the
submucosa and thence the muscularis propria. Tumor
cells describe irregular tubular structures,
harboring pluristratification, multiple lumens,
reduced stroma ("back to back" aspect). Sometimes,
tumor cells are discohesive and secrete mucus which
invades the interstitium producing large pools of
mucus/colloid (optically "empty" spaces) - mucinous
(colloid) adenocarcinoma, poorly differentiated. If
the mucus remains inside the tumor cell, it pushes
the nucleus at the periphery - "signet-ring cell".
Depending on glandular architecture, cellular
pleomorphism and mucosecretion of the predominant
pattern, adenocarcinoma may present 3 degrees of
differentiation: well, moderate and poorly
differentiate.
Stages of
Colon Cancer
TNM or Duke's Colon cancer staging
is an estimate of the condition
of a particular cancer for diagnostic and research
purposes.
The systems for staging
colorectal cancers (colon cancers)
largely depend on the extent of local invasion, the
degree of
lymph node involvement and whether there
is distant metastasis.
The most common currently
used system for staging colon cancers is the TNM system, though
many doctors still use the older Duke's system. The
TNM system assigns a number:
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