What is colon cancer?
Colon cancer starts in the colon or rectum. These cancers can also be called colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often in the same group because they have many features in common in the colon and rectum.
The large intestine and rectum make up the large intestine, which is part of the gastrointestinal tract, also called the gastrointestinal tract (GI).
How does colon cancer start?
Polyps in the large intestine or rectum
Most colorectal cancers begin as the inner lining of the colon or rectum grows. These growths are called polyps.
Some types of polyps can become cancerous over time (usually years), but not all polyps can become cancerous. The likelihood of a polyp turning into cancer depends on the type of polyp. There are different types of polyps
Adenomatous polyp (adenoma):
These polyps sometimes turn into cancer. For this reason, an adenoma is called a precancerous disease. There are 3 types of adenoma: tubular, villous and tubular.
Hypplastic polyps and inflammatory polyps:
These polyps are more common, but are generally not precancerous. Some people with large hypoplastic polyps (more than 1 cm) may need to be screened for colon cancer by colonoscopy.
Immobile dentate polyps (SSP) and traditional dentate adenomas: (TSA)
These polyps are often treated like adenomas because they carry a higher risk of colon cancer.
Other factors that increase the risk of colon cancer or increase the risk of colon cancer include:
- If a polyp larger than 1 cm is found
- If more than 3 polyps are found
- If it is observed in the polyp after the dysplasia is gone.
Dysplasia is another precancerous condition.
This means that there is an area in the polyp or lining of the colon or rectum where the cells look abnormal but have not turned into cancer.
How colon cancer spreads:
If cancer develops in a polyp, it can grow into the wall of the colon or rectum over time. The wall of the large intestine and rectum are composed of many layers. Colon cancer starts in the innermost layer (mucosa) and can grow out through some or all of the other layers.
Once cancer cells are in the wall, they can turn into blood vessels or lymphatic vessels (small canals that carry waste and fluid). From there, they can travel to the surrounding lymph nodes or to distant parts of the body.
The stage (prevalence) of colorectal cancer depends on how deep it grows in the wall and how it spreads outside the colon or rectum.
Types of cancer in the colon and rectum
- Adenocarcinoma of the colon:
These cancers occur in cells that make mucus to lubricate the colon and rectum. When doctors talk about colon cancer, they almost always talk about it. Some subtypes of adenocarcinoma, such as ringworm and mucus, may have a worse prognosis than other subtypes of adenocarcinoma.
Other types of tumors that are much less common can also start in the large intestine and rectum.
Which includes the following tumors:
These cells start with specific hormone-producing cells in the gut. See Gastrointestinal carcinoid tumors.
Gastrointestinal stromal tumors
(GIST) starts with specific cells in the wall of the large intestine called Cajal interstitial cells. Some are benign (not cancer). These tumors are found everywhere in the gastrointestinal tract but are not common in the large intestine
Cancer is the cells of the immune system. They mostly start in the lymph nodes, but can also start in the large intestine, rectum or other organs. Information on gastrointestinal lymphomas can be found in non-Hodgkin’s lymphoma.
It can start in blood vessels, muscle layers or other connective tissues in the wall of the large intestine and rectum. Colon or rectal sarcoma is rare.
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