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Colon cancer is malignant cells found in the colon or rectum. The colon and the rectum are parts of the large intestine, which is part of the digestive system. Because colon cancer and rectal cancers have many features in common, they are sometimes referred to together as colorn cancer. Cancerous tumors found in the colon or rectum also may spread to other parts of the body.
Excluding skin cancers, colon cancer is the third most common cancer in both men and women. The American Cancer Society estimates that about 140,000 colon cancer cases and about 50,000 deaths from colon cancer occur each year. The number of deaths due to colon cancer has decreased, which is attributed to increased screening and polyp removal and to improvements in cancer treatment.
A type of cancer called adenocarcinoma accounts for more than 95 percent of cancers in the colon and rectum and is usually what is meant by the term colorectal cancer. It is the type we focus on in this section. There are other types of cancer that can be found in the colon and rectum, but they are rare.
Here is an overview of the types of cancer in the colon and rectum:
Adenocarcinoma. Adenocarcinomas are tumors that start in the lining of internal organs. Adeno means gland. These tumors start in cells with glandular properties, or cells that secrete. They can form in many different organs, such as the lung or the breast. In colorectal cancer, early tumors start as small adenomatous polyps that continue to grow and can then turn into malignant tumors. The vast majority of colorectal cancers are adenocarcinomas.
Gastrointestinal stromal tumors (GIST). These are tumors that start in specialized cells in the wall of the digestive tract called the interstitial cells of Cajal. These tumors may be found anywhere in the digestive tract, although they rarely appear in the colon. They can be benign (noncancerous) at first, but many do turn into cancer. When this happens, they are called sarcomas. Surgery is the usual treatment if the tumor has not spread.
Lymphoma. A lymphoma is a cancer that typically starts in a lymph node, which is part of the immune system. However, it can also start in the colon, rectum, or other organs.
Carcinoids. Carcinoids are tumors that start in special hormone-producing cells in the intestine. Often they cause no symptoms at first. Surgery is the usual treatment.
Sarcoma. Tumors that start in blood vessels, muscle, or connective tissue in the the colon and rectum wall.
The following are the most common colon cancer symptoms. However, each individual may experience symptoms differently.
People who have any of the following symptoms should check with their doctors, especially if they are over 50 years old or have a personal or family history of the disease:
A change in bowel habits such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days
Rectal bleeding, dark stools, or blood in the stool
Cramping or gnawing stomach pain
Unintended weight loss
Weakness and fatigue
A feeling that you need to have a bowel movement that is not relieved by doing so
The symptoms of colon cancer may resemble other conditions, such as infections, hemorrhoids, and inflammatory bowel disease. It is also possible to have colon cancer and not have any symptoms. Always consult your health care provider for a diagnosis.
Risk factors may include:
Age. Most people who have colon cancer are over age 50; however, it can occur at any age.
Race and ethnicity. African-Americans have the highest risk for colon cancer of all racial groups in the U.S. Jews of Eastern European descent (Ashkenazi Jews) have the highest colon cancer risk of any ethnic group in the world.
Diet. Colon cancer is often associated with a diet high in red and processed meats.
Personal history of colorectal polyps. Benign growths on the wall of the colon or rectum are common in people over age 50, and may lead to colon cancer.
Personal history of colon cancer. People who have had colon cancer have an increased risk for another colon cancer.
Family history. People with a strong family history of colon cancer or polyps in a first-degree relative (especially in a parent or sibling before the age of 45 or in two first-degree relatives of any age) have an increased risk for colon cancer.
Ulcerative colitis or Crohn's disease. People who have an inflamed lining of the colon have an increased risk for colorectal cancer.
Inherited syndromes, such as familial adenomatous polyposis or hereditary nonpolyposis colon cancer, also known as Lynch syndrome
Heavy alcohol consumption
Type 2 diabetes
The exact cause of most colon cancer is unknown, but the known risk factors listed above are the most likely causes. A small percentage of colon cancers are caused by inherited gene mutations. People with a family history of colorectal cancer may wish to consider genetic testing. The American Cancer Society suggests that anyone undergoing such tests have access to a doctor or geneticist qualified to explain the significance of these test results.
Although the exact cause of colon cancer is not known, it may be possible to lower your risk of colon cancer with the following:
Diet, weight, and exercise. It is important to manage the risk factors you can control, such as diet, body weight, and exercise. Eating more fruits, vegetables, and whole-grain foods, and limiting red and processed meats, plus exercising appropriately, even small amounts on a regular basis, can be helpful. Avoiding excess alcohol intake may also lower your risk.
Drug therapy. Some studies have shown that low doses of nonsteroidal anti-inflammatory drugs, such as aspirin, and hormone replacement therapy for postmenopausal women, may reduce the risk of colon cancer. But these drugs also have their own potentially serious risks, so it is important to discuss this with your health care provider.
Screenings. Perhaps most important to the prevention of colon cancer is having screening tests at appropriate ages. Screening may find some colorectal polyps that can be removed before they have a chance to become cancerous. Because some colorectal cancers cannot be prevented, finding them early is the best way to improve the chance of successful treatment, and reduce the number of deaths caused by colon cancer.
The following screening guidelines can lower the number of cases of the disease, and can also lower the death rate from colorectal cancer by detecting the disease at an earlier, more treatable stage.
Screening methods for colon cancer, for people who do not have any symptoms or strong risk factors, include the following:
Fecal occult blood test (FOBT). Checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then sent to a laboratory.
Fecal immunochemical test (FIT). A test that is similar to a FOBT, but does not require any restrictions on diet or medications prior to the test.
Flexible sigmoidoscopy. A diagnostic procedure that allows the doctor to examine the inside of a portion of the large intestine. A short, flexible, lighted tube with a small video camera on the end, called a sigmoidoscope, is inserted into the intestine through the rectum. The scope blows air into the intestine to inflate it and make viewing the inside easier.
Colonoscopy. A procedure that allows the doctor to view the entire length of the large intestine, and can often help identify abnormal growths, inflamed tissue, ulcers, and bleeding. It involves inserting a colonoscope, a long, flexible, lighted tube, in through the rectum up into the colon. The colonoscope allows the doctor to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.
CT colonography (virtual colonoscopy). A procedure that uses computerized tomography (CT) scans to examine the colon for polyps or masses. The images are processed by a computer to make a three-dimensional (3-D) model of the colon. Virtual colonoscopy is noninvasive, although it requires a small tube to be inserted into the rectum to pump air into the colon. If something abnormal is seen with this test, a standard colonoscopy will be needed as follow up.
Barium enema with air contrast (also called a double contrast barium enema). A fluid called barium (a metallic, chemical, chalky liquid used to coat the inside of organs so that they will show up on an X-ray) is administered into the rectum to partially fill up the colon. Air is then pumped in to expand the colon and rectum. An X-ray of the abdomen is then taken and can show strictures (narrowed areas), obstructions (blockages), and other problems.
Screening guidelines for colon cancer
Colon cancer screening guidelines from the American Cancer Society for early detection include:
Beginning at age 50, both men and women should follow one of the examination schedules below:
Fecal occult blood test or fecal immunochemical test every year
Flexible sigmoidoscopy every five years
Double-contrast barium enema every five years
Colonoscopy every 10 years
CT colonography (virtual colonoscopy) every five years
People with any of the following colorectal cancer risk factors should begin screening procedures at an earlier age and/or be screened more often:
Strong family history of colorectal cancer or polyps in a first-degree relative, especially in a parent or sibling before the age of 45 or in two first-degree relatives of any age
Family with hereditary colorectal cancer syndromes, such as familial adenomatous polyposis and hereditary nonpolyposis colon cancer
Personal history of colorectal cancer or adenomatous polyps
Personal history of chronic inflammatory bowel disease (Crohn's disease or ulcerative colitis)
If a person has symptoms that might be caused by colon cancer, the doctor will want to get a complete medical history and do a physical examination. The doctor may also do certain tests to look for cancer. Many of these tests are the same as those done to screen for colon cancer in people without symptoms.
Digital rectal examination. A doctor or other health care provider inserts a gloved and lubricated finger into the rectum to feel for anything unusual or abnormal. This test can detect some cancers of the rectum, but not the colon.
Fecal occult blood test. This test checks for hidden (occult) blood in the stool. It involves placing a very small amount of stool on a special card, which is then sent to a laboratory.
Colonoscopy. A procedure that allows the doctor to view the entire length of the large intestine. It involves inserting a colonoscope, a long, flexible, lighted tube, in through the rectum up into the colon. The colonoscope allows the doctor to see the lining of the colon, remove tissue for further examination, and possibly treat some problems that are discovered.
Barium enema (also called double contrast barium enema). A fluid called barium (a metallic, chemical, chalky liquid used to coat the inside of organs so that they will show up on an X-ray) is administered into the rectum to partially fill up the colon. An X-ray of the abdomen is then taken that can show strictures (narrowed areas), obstructions (blockages), and other problems.
Biopsy. a procedure in which polyps or tissue samples are removed (during a colonoscopy or surgery) from the body for examination under a microscope to determine if cancer or other abnormal cells are present.
Blood count. A test to check for anemia (that can be a result of bleeding from a tumor).
Imaging tests. Tests, such as a CT scan, PET scan, ultrasound, or MRI of the abdomen, may be done to look for tumors or other problems. These tests may also be done if colon cancer has already been diagnosed to help determine the extent (stage) of the cancer.
When colon cancer is diagnosed, tests will be performed to determine how much cancer is present, and if the cancer has spread from the colon or rectum to other parts of the body. This is called staging, and it is an important step toward planning a treatment program. The stages for colon cancer are as follows:
Stage 0 (Cancer in situ)
The cancer is found in the innermost lining of the colon or rectum.
Stage I (also called Dukes' A colon cancer)
The cancer has spread beyond the innermost lining of the colon or rectum to the second and third layers. The cancer has not spread to the outer wall or outside of the colon or rectum.
Stage II (also called Dukes' B colon cancer)
The cancer has spread through into the wall or outside the colon or rectum to nearby tissue. However, the lymph nodes are not involved.
Stage III (also called Dukes' C colon cancer)
The cancer has spread to nearby lymph nodes, but has not spread to other organs in the body.
Stage IV (also called Dukes' D colon cancer)
The cancer has spread to other parts of the body, such as the lungs.
Specific treatment for colon cancer will be determined by your doctor based on:
Your age, overall health, and medical history
Extent and location of the disease
Results of certain lab tests
Your tolerance for specific medications, procedures, or therapies
Expectations for the course of this disease
Your opinion or preference
After the colon cancer is diagnosed and staged, your doctor will recommend a treatment plan. Treatment may include:
Colon surgery. Often, the primary treatment for colon cancer is an operation, in which the cancer and a length of normal tissue on either side of the cancer are removed, as well as the nearby lymph nodes.
Radiation therapy. Radiation therapy is the use of high-energy radiation to kill cancer cells and to shrink tumors. There are two ways to deliver radiation therapy, including the following:
External radiation (external beam therapy). A treatment that precisely sends high levels of radiation directly to the cancer cells. The machine is controlled by the radiation therapist. Since radiation is used to kill cancer cells and to shrink tumors, special shields may be used to protect the tissue surrounding the treatment area. Radiation treatments are painless and usually last a few minutes.
Internal radiation (brachytherapy, implant radiation). Radiation is given inside the body as close to the cancer as possible. Radioactive material is placed next to or directly into the cancer, which limits the effects of surrounding healthy tissues. Some of the radioactive implants are called seeds or capsules.Internal radiation involves giving a higher dose of radiation in a shorter time span than with external radiation. Some internal radiation treatments stay in the body temporarily. Other internal treatments stay in the body permanently, though the radioactive substance loses its radiation within a short period of time. In some cases, both internal and external radiation therapies are used.
Chemotherapy. Chemotherapy is the use of anticancer drugs to treat cancerous cells. In most cases, chemotherapy works by interfering with the cancer cell's ability to grow or reproduce. Different groups of drugs work in different ways to fight cancer cells. The oncologist will recommend a treatment plan for each individual. Studies have shown that chemotherapy after surgery may increase the survival rate for patients with some stages of colon cancer. It can also be helpful before or after surgery for some stages of rectal cancer. Chemotherapy can also help slow the growth or relieve symptoms of advanced cancer.
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