Start and spread of colorectal cancer
If cancer forms in a polyp, it can eventually begin to grow into the wall of the colon or rectum. When cancer cells are in the wall, they can then grow into blood vessels or lymph vessels. Lymph vessels are thin, tiny channels that carry away waste and fluid. They first drain into nearby lymph nodes, which are bean-shaped structures containing immune cells that help fight against infections. Once cancer cells spread into blood or lymph vessels, they can travel to nearby lymph nodes or to distant parts of the body, such as the liver. Spread to distant parts of the body is called metastasis.
Types of cancer in the colon and rectum
Several types of cancer can start in the colon or rectum.
Adenocarcinomas: More than 95% of colorectal cancers are a type of cancer known as adenocarcinomas. These cancers start in cells that form glands that make mucus to lubricate the inside of the colon and rectum. When doctors talk about colorectal cancer, this is almost always what they are referring to.
Other, less common types of tumors may also start in the colon and rectum. These include:
Carcinoid tumors: These tumors start from specialized hormone-producing cells in the intestine. They are discussed in our document, Gastrointestinal Carcinoid Tumors.
Gastrointestinal stromal tumors (GISTs): These tumors start from specialized cells in the wall of the colon called theinterstitial cells of Cajal. Some are benign (non-cancerous); others are malignant (cancerous). These tumors can be found anywhere in the digestive tract, but they are unusual in the colon. They are discussed in our document, Gastrointestinal Stromal Tumors (GIST).
Lymphomas: These are cancers of immune system cells that typically start in lymph nodes, but they may also start in the colon, rectum, or other organs. Information on lymphomas of the digestive system is included in our document, Non-Hodgkin Lymphoma.
Sarcomas: These tumors can start in blood vessels as well as in muscle and connective tissue in the wall of the colon and rectum. Sarcomas of the colon or rectum are rare. They are discussed in our document, Sarcoma - Adult Soft Tissue Cancer.
The remainder of this document focuses only on adenocarcinoma of the colon and rectum.
Inherited syndromes
About 5% to 10% of people who develop colorectal cancer have inherited gene defects (mutations) that cause the disease. Often, these defects lead to cancer that occurs at a younger age than is common. Identifying families with these inherited syndromes is important because it lets doctors recommend specific steps, such as screening and other preventive measures when the person is younger.
Several types of cancer can be linked with these syndromes, so it's important to check your family medical history not just for colon cancer and polyps, but also for any other type of cancer. While cancer in close (first-degree) relatives is most concerning, any history of cancer in more distant relatives is also important. This includes aunts, uncles, grandparents, nieces, nephews, and cousins. People who know they have a family history of cancer or colorectal polyps should discuss this history with their doctor. They may benefit from genetic counseling to review their family medical tree to see how likely it is that they have a family cancer syndrome and a discussion about whether or not gene testing is right for them. People who have an abnormal gene can take steps to prevent colon cancer, such as getting screened and treated at an early age. More information on genetic counseling and testing can be found in the section, “Can colorectal cancer be prevented?”
The 2 most common inherited syndromes linked with colorectal cancers are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).
Familial adenomatous polyposis (FAP): FAP is caused by changes (mutations) in the APC gene that a person inherits from his or her parents. About 1% of all colorectal cancers are due to FAP.
People with FAP typically develop hundreds or thousands of polyps in their colon and rectum, usually in their teens or early adulthood. Cancer usually develops in 1 or more of these polyps as early as age 20. By age 40, almost all people with this disorder will have developed cancer if preventive surgery (removing the colon) is not done.
Gardner syndrome is a type of FAP that also has benign (non-cancerous) tumors of the skin, soft connective tissue, and bones.
Hereditary non-polyposis colon cancer (HNPCC): HNPCC, also known as Lynch syndrome, accounts for about 3% to 5% of all colorectal cancers. HNPCC can be caused by inherited changes in a number of different genes that normally help repair DNA damage. (See the section, “Do we know what causes colorectal cancer?” for more details.)
The cancers in this syndrome also develop when people are relatively young, although not as young as in FAP . People with HNPCC may also have polyps, but they only have a few, not hundreds as in FAP. The lifetime risk of colorectal cancer in people with this condition may be as high as 80%.
Women with this condition also have a very high risk of developing cancer of the endometrium (lining of the uterus). Other cancers linked with HNPCC include cancer of the ovary, stomach, small bowel, pancreas, kidney, brain, ureters (tubes that carry urine from the kidneys to the bladder), and bile duct.
For more information on HNPCC, see the sections, “Do we know what causes colorectal cancer?” and “Can colorectal cancer be prevented?”
Turcot syndrome: This is a rare inherited condition in which people are at increased risk of adenomatous polyps and colorectal cancer, as well as brain tumors. There are actually 2 types of Turcot syndrome:
- One can be caused by gene changes similar to those seen in FAP, in which cases the brain tumors are medulloblastomas.
- The other can also be caused by gene changes similar to those seen in HNPCC, in which cases the brain tumors are glioblastomas.
Peutz-Jeghers syndrome: People with this rare inherited condition tend to have freckles around the mouth (and sometimes on the hands and feet) and a special type of polyp in their digestive tracts (called hamartomas). They are at greatly increased risk for colorectal cancer, as well as several other cancers, which usually appear at a younger than normal age. This syndrome is caused by mutations in the gene STK1.
MUTYH-associated polyposis: People with this syndrome develop colon polyps which will become cancerous if the colon is not removed. They also have an increased risk of cancers of the small intestine skin, ovary, and bladder. This syndrome is caused by mutations in the gene MUTYH.
I apologize for all of the copied information, but it is better to be well informed rather than me tell you the limited amount I know. For more information, also look at the Susan Cohan Colon Cancer Foundation.
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| Susan Cohan and Family |
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