## Colorectal cancer (also known as
colon cancer, rectal cancer or bowel cancer) is the development of cancer in
the colon or rectum (parts of the large intestine). It is due to the abnormal
growth of cells that have the ability to invade or spread to other parts of the
body. Signs and symptoms may include blood in the stool, a change in bowel
movements, weight loss, and feeling tired all the time.
## Risk factors for colorectal
cancer include lifestyle, older age, and inherited genetic disorders. Other
risk factors include diet, smoking, alcohol, lack of physical activity, family
history of colon cancer and colon polyps, presence of colon polyps, race,
exposure to radiation, and even other diseases such as diabetes and obesity.
Genetic disorders only occur in a small fraction of the population. A diet high
in red, processed meat, while low in fiber increases the risk of colorectal
cancer. Other diseases such as inflammatory bowel disease, which includes
Crohn’s disease and ulcerative colitis, can increase the risk of colorectal cancer.
Some of the inherited genetic disorders that can cause colorectal cancer
include familial adenomatous polyposis and hereditary non-polyposis colon
cancer; however, these represent less than 5% of cases. It typically starts as
a benign tumor, often in the form of a polyp, which over time becomes
cancerous.
## Treatments used for colorectal cancer may include some combination
of surgery, radiation therapy, chemotherapy and targeted therapy. Cancers that
are confined within the wall of the colon may be curable with surgery while
cancer that has spread widely are usually not curable, with management focusing
on improving quality of life and symptoms. Five year survival rates in the
United States are around 65%. This, however, depends on how advanced the cancer
is, whether or not all the cancer can be removed with surgery, and the person’s
overall health. Globally, colorectal cancer is the third most common type of
cancer making up about 10% of all cases. In 2012 there were 1.4 million new
cases and 694,000 deaths from the disease. It is more common in developed
countries, where more than 65% of cases are found. It is less common in women
than men
Types of Colorectal Cancer
## Adenocarcinoma is the most common type of colorectal cancer. Other
colorectal cancers include gastrointestinal carcinoid tumours, gastrointestinal
stromal tumours, primary colorectal lymphoma, leiomyosarcoma, melanoma and
squamous cell carcinoma.
Colorectal adenocarcinoma
A cancer of the
intestinal gland cells, adenocarcinomas represent more than 95 percent of colon
and rectal cancers. “Adeno” is the prefix for gland, and adenocarcinomas
typically start within the intestinal gland cells that line the inside of the
colon and/or rectum. They tend to start in the inner layer and then spread
deeper to other layers. There are two main subtypes of adenocarcinoma:
Mucinous adenocarcinoma is
made up of approximately 60 percent mucus. The mucus can cause cancer cells to
spread faster and become more aggressive than typical adenocarcinomas. Mucinous
adenocarcinomas account for 10 to 15 percent of all colon and rectal
adenocarcinomas.
Signet ring cell adenocarcinoma accounts for less than one percent of
adenocarcinomas. Named for its appearance under a microscope, signet ring cell
adenocarcinoma is typically aggressive and may be more difficult to treat.
Other types of colorectal cancer
There are many other
types of rare colorectal cancers, and combined these types account for just 5
percent of all cases. Below are examples of other colorectal types:
Gastrointestinal carcinoid tumors: This slow-growing cancer forms in the
neuroendocrine cell (a nerve cell that also creates hormones) in the lining of
the gastrointestinal tract. These tumors account for just 1 percent of all
colorectal cancers, but half of all of the cancers found in the small
intestine.
Primary colorectal lymphomas: A
type of non-Hodgkin lymphoma (NHL), lymphomas are cancers that develop in the
lymphatic system from cells called lymphocytes. Lymphocytes are a type of white
blood cell that helps the body fight infections. NHL can develop in many parts
of the body, including the lymph nodes, bone marrow, spleen, thymus and the
digestive tract. Primary colorectal lymphomas account for just 0.5 percent of
all colorectal cancers, and about 5 percent of all lymphomas. The disease
usually occurs later in life, and is more common in men than women.
Gastrointestinal stromal tumors: Also known as GISTs, this is a rare type
of colorectal cancer that starts in a special cell found in the lining of the
gastrointestinal (GI) tract called interstitial cells of Cajal (ICCs). More
than 50 percent of GISTs start in the stomach. While most of the others start
in the small intestine, the rectum is the third most common location. GISTs are
classified as sarcomas, cancers that begin in the connective tissues, which
include fat, muscle, blood vessels, deep skin tissues, nerves, bones and
cartilage.
Leiomyosarcomas: Another form of sarcoma, leiomyosarcomas
essentially means “cancer of smooth muscle.” The colon and rectum have three
layers of the type of muscle that can be affected, which all work together to
guide waste through the digestive tract. This rare type of colorectal cancer
accounts for about 0.1 percent of all colorectal cases.
Melanomas: Though most commonly associated with the skin,
melanomas can occur anywhere, including the colon or rectum.
Squamous cell carcinomas: Some parts of the GI tract, like the
upper part of the esophagus and the end of the anus, are lined with flat cells
called squamous cells. These are the same type of cells that are found on the
surface of the skin. Cancers starting in these cells are called squamous cell
carcinoma.
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