https://www.cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html#references
What Is Colorectal Cancer?
Colorectal cancer is a cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Cancer starts when cells in the body start to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
How does colorectal cancer start?
Polyps in the colon or rectum
Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps.
Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp changing into cancer depends on the type of polyp it is. The 2 main types of polyps are:
Adenomatous polyps (adenomas): These polyps sometimes change into cancer. Because of this, adenomas are called a pre-cancerous condition.
Hyperplastic polyps and inflammatory polyps: These polyps are more common, but in general they are not pre-cancerous.
Other factors that can make a polyp more likely to contain cancer or increase someone’s risk of developing colorectal cancer include:
If a polyp larger than 1 cm is found
If more than 2 polyps are found
If dysplasia is seen in the polyp after it’s removed. Dysplasia is another pre-cancerous condition. It means there’s an area in a polyp or in the lining of the colon or rectum where the cells look abnormal, but they don’t look like true cancer cells.
For more details on the types of polyps and conditions that can lead to colorectal cancer, see Understanding Your Pathology Report: Colon Polyps.
How colorectal cancer spreads
If cancer forms in a polyp, it can grow into the wall of the colon or rectum over time. The wall of the colon and rectum is made up of many layers. Colorectal cancer starts in the innermost layer (the mucosa) and can grow outward through some or all of the other layers.
When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels (tiny channels that carry away waste and fluid). From there, they can travel to nearby lymph nodes or to distant parts of the body.
The stage (extent of spread) of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum. For more on staging, see Colorectal Cancer Stages.
Where does colorectal cancer grow?
To understand colorectal cancer, it helps to understand the parts that make up the colon and rectum. The colon and rectum make up the large intestine (or large bowel), which is part of the digestive system, also called the gastrointestinal (GI) system (see illustration below).
What Is Colorectal Cancer?
Colorectal cancer is a cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.
Cancer starts when cells in the body start to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?
How does colorectal cancer start?
Polyps in the colon or rectum
Most colorectal cancers start as a growth on the inner lining of the colon or rectum. These growths are called polyps.
Some types of polyps can change into cancer over time (usually many years), but not all polyps become cancer. The chance of a polyp changing into cancer depends on the type of polyp it is. The 2 main types of polyps are:
Adenomatous polyps (adenomas): These polyps sometimes change into cancer. Because of this, adenomas are called a pre-cancerous condition.
Hyperplastic polyps and inflammatory polyps: These polyps are more common, but in general they are not pre-cancerous.
Other factors that can make a polyp more likely to contain cancer or increase someone’s risk of developing colorectal cancer include:
If a polyp larger than 1 cm is found
If more than 2 polyps are found
If dysplasia is seen in the polyp after it’s removed. Dysplasia is another pre-cancerous condition. It means there’s an area in a polyp or in the lining of the colon or rectum where the cells look abnormal, but they don’t look like true cancer cells.
For more details on the types of polyps and conditions that can lead to colorectal cancer, see Understanding Your Pathology Report: Colon Polyps.
How colorectal cancer spreads
If cancer forms in a polyp, it can grow into the wall of the colon or rectum over time. The wall of the colon and rectum is made up of many layers. Colorectal cancer starts in the innermost layer (the mucosa) and can grow outward through some or all of the other layers.
When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels (tiny channels that carry away waste and fluid). From there, they can travel to nearby lymph nodes or to distant parts of the body.
The stage (extent of spread) of a colorectal cancer depends on how deeply it grows into the wall and if it has spread outside the colon or rectum. For more on staging, see Colorectal Cancer Stages.
Where does colorectal cancer grow?
To understand colorectal cancer, it helps to understand the parts that make up the colon and rectum. The colon and rectum make up the large intestine (or large bowel), which is part of the digestive system, also called the gastrointestinal (GI) system (see illustration below).
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