More than 95 percent of colorectal cancers are adenocarcinomas — cancers of the cells that line the interior of the colon and rectum. Rarer types of tumors include carcinoid tumors, gastrointestinal tumors, and lymphomas.
The type of colorectal cancer you’re diagnosed with will help your physicians decide on the best way to treat your cancer. Depending on whether you are diagnosed with colon cancer or rectal cancer, your treatment may be slightly different. Because rectal cancer surgery is more complex, due to the narrow confines of the pelvis, we take special care to avoid damaging sexual and bladder nerves as well as a colostomy (bag).
Genetics and colorectal cancers
Only about five to 10 percent of colorectal cancers are passed from parents to their children though it is possible. Several gene mutations, or abnormalities, that cause colorectal cancer, and allow it to be transmitted to family members, have been found.
The two most common inherited colorectal cancer syndromes are hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). They can affect both men and women, and the children of people who carry these genes have a 50 percent chance of inheriting the disease-causing gene.
This is the most common form of hereditary colorectal cancer, accounting for about three percent of all colorectal cancer diagnoses each year. If you’ve been diagnosed with HNPCC, chances are you have at least three family members and two generations with colorectal cancer, with cancer that develops before age 50. Although not everyone who inherits the HNPCC gene will develop colorectal cancer, the risk is very high -- about 80 percent. People with HNPCC also have a higher risk of developing other cancers, such as kidney, ovarian, uterine, renal pelvis, small intestine, and stomach cancer.
We can evaluate the pattern of colorectal cancer in your family in order to determine if the family has HNPCC. Families considered to be "HNPCC families" must display certain criteria indicating a pattern of colon cancer throughout generations. These are referred to as the Amsterdam Criteria, and include:
- At least three members (two in small families) with colon or rectal cancer or two members with colorectal cancer and one with endometrial cancer, with other early-onset Lynch syndrome defined cancer.
- At least two successive generations with colon or rectal cancer.
- Two family members with the disease are first-degree relatives (i.e. parents, brothers, sisters or children) of another family member with colon and rectal cancer.
- At least one member affected at or before age 50.
- The familial adenomatous polyposis syndrome is excluded from the family member's diagnosis.
Colonoscopies are recommended in family members who are 10 years younger than the youngest family member who was diagnosed with cancer.
Familial adenomatous polyposis (FAP) is a rare condition characterized by the presence of more than hundreds or even thousands of benign polyps, or growths in the large intestine. It is thought to be present in about one percent of all people diagnosed with colorectal cancer each year. The polyps occur early in life, with 95 percent of people with FAP developing polyps by age 35, and are often detected in patients in their teens, with 50 percent developing polyps by age 15. If the colon is not surgically removed, there is a 100 percent chance that some of the polyps will develop into cancer, usually by age 40.
While most cases of FAP are inherited, nearly a third of the cases are the result of a spontaneous or newly-occurring gene mutation, or abnormality. For those who develop a new gene mutation, it is possible to pass the FAP gene onto their children.
Genes are tiny segments of DNA that control how cells function, such as telling them when to divide and grow. One copy of each gene comes from your mother; the other comes from your father.
In 1991, researchers made a significant breakthrough in the diagnosis of FAP. They identified the gene - called APC - that is responsible for the condition. This gene mutation can be detected in 82 percent of patients with FAP. The exact lifetime risk of developing colon cancer in people who have inherited this gene abnormality is about 100 percent. Families in which this gene mutation occurs may or may not have one or more family members with colorectal cancer or polyps.
Types of tumors
- Adenocarcinoma is the type of cancer cell found in 90 to 95 percent of colon cancer cases. Adenocarcinoma forms from the cells that help produce the mucus that lines the colon or rectum. They can invade the wall of the colon and then spread via lymphatic channels to surrounding lymph nodes. From there they can spread to the liver and the lungs.
- Carcinoid tumors and neuroendocrine tumors typically occur in the small intestine and appendix and occasionally the rectum. They rarely occur in the colon.
- Gastrointestinal stromal tumors can form anywhere in the digestive tract, though rarely in the colon. They can start in the special cells found in the wall of the GI tract, called the interstitial cells of Cajal (ICCs). ICCs are cells of the autonomic nervous system, the part of the nervous system that regulates body processes such as digesting food. ICCs are sometimes called the “pacemakers” of the GI tract because they signal the muscles in the digestive system to contract to move food and liquid through the GI tract.
More than half of gastrointestinal stromal tumors start in the stomach. Most of the others start in the small intestine, but these types of tumors can start anywhere along the GI tract. A small number start outside the GI tract in nearby areas such as the omentum (an apron-like layer of fatty tissue that hangs over the organs in the abdomen) or the peritoneum (the layer of tissue that lines the organs and walls of the abdomen).
Not all gastrointestinal stromal tumors are cancerous. Some are benign (not cancerous) and don’t grow into other areas or spread to other parts of the body.
- Lymphomas are cancers of immune system cells. They rarely begin in the colon or rectum.
Recurrent colorectal cancer is cancer that has disappeared after treatment but has now come back, either in or near the colon or rectum, or in other organs.