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Colon and rectal Cancer
 Colorectal cancer is the term used for cancers arising in the colon or rectum. The colon and rectum form the large intestine, the part of the body’s digestive system where waste material is stored. The large intestine, also called the large bowel, is about five to six feet long. It absorbs water from stool and changes it from a liquid to a solid form.
Colon cancers are cancers that form in the mucosal lining of the colon. Rectal cancers are cancers that form in the tissues of the rectum, the last six to ten inches of the large intestine before the anus. About 150,000 people are diagnosed with colon cancer every year in the United States, making it the third most common type of cancer. Although cancers of the colon and the rectum are similar, they may be treated differently because of the anatomic location where they start.
About 95 percent of colorectal cancers are adenocarcinomas, which are cancers that begin in cells that line the large intestine and make and release mucus and other fluids. No one knows the exact causes of colorectal cancer. Tumors of the colon and rectum usually begin in the inner wall of the large intestine.
Most cancers of the large intestine are believed to have developed from polyps. Polyps are benign tumors of the large intestine. Polyps are not life threatening, and they can be easily removed during a colonoscopy, a common screening test for colon cancer. There is strong evidence though that patients who form multiple polyps in their colon or rectum are at higher risk for developing colorectal cancer. If benign polyps are not removed from the large intestine, they can become cancerous over time. Finding and removing polyps are now known to be important in preventing colorectal cancer. The American Cancer Society recommends a baseline colonoscopy when people reach age 50 and then every 10 years or so, depending upon the findings. This is especially true for individuals who have a history of colon or rectal cancer in their family.
Colorectal cancer can be present for several years before symptoms develop. Symptoms vary according to where in the large intestine the tumor is located. The right side of the colon is large, and cancers of the right colon can grow to large sizes before they cause any abdominal symptoms. Usually, right-sided cancers cause iron deficiency anemia due to the slow loss of blood over a long period of time. Iron deficiency anemia causes fatigue, weakness, and shortness of breath.
The left side of the colon is narrower than the right colon. Cancers of the left colon are more likely to cause partial or complete bowel obstruction. Cancers causing partial bowel obstruction can cause constipation, narrow stools, diarrhea, abdominal pains, cramps, and bloating. Bright red blood in the stool may also indicate a growth near the end of the left colon or rectum.
Many treatments are available for colorectal cancer and selecting the best one for an individual person with colorectal cancer depends on the stage of disease. Identifying the stage of colorectal cancer is also important because it provides information to help the doctor predict the prognosis (outcome) for the patient. The doctor will classify a patient’s colorectal cancer on the basis of the results of imaging studies but the final stage is not usually known until after surgery has been done to remove the primary tumor and a pathologist has examined the tumor specimen and the nearby lymph nodes that were removed.
The most commonly used system used to help describe the stage of cancer is the tumor, node, metastasis (TNM) classification developed by the American Joint Committee on Cancer (AJCC). This system allows the doctor and pathologist to determine how deeply the tumor has grown into the layers of tissue that line the inside of the colon or rectum (the T category), whether there are cancer cells in nearby lymph nodes (the N category) and whether the cancer has spread to other parts of the body (the M category) (Table 1).
Once the cancer has been classified according to this system, an overall stage is assigned. There are five stages (designated as 0 to IV), and stages II and III are further classified according to how deeply the tumor extends into the lining of the colon or rectum (Table 2).
| Classification |
Definition |
| Tumor (T) |
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| Tx |
Tumor cannot be evaluated (because of lack of information) |
| Tis |
Carcinoma in situ; cancer cells are found only in the mucosa, the first layer of the lining of the colon or rectum |
| T1 |
The tumor has grown into the submucosa, the second layer of the lining |
| T2 |
The tumor has grown into the muscularis propria, the third layer of the lining |
| T3 |
The tumor has grown into the subserosa, the deepest layer of the lining, or into tissues surrounding the colon or rectum |
| T4 |
The tumor has grown through the wall of the colon or rectum and into nearby tissues or organs
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| Nearby Nodes (N) |
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| Nx |
Nearby (regional) lymph nodes cannot be evaluated (because of lack of information)
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| N0 |
No cancer cells are found in nearby lymph nodes
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| N1 |
Cancer cells are found in 1, 2 or 3 nearby lymph nodes
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| N2 |
Cancer cells are found in at least 4 nearby lymph nodes
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| Distant Metastasis (M) |
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| Mx |
Metastasis cannot be evaluated (because of lack of information)
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| M0 |
No distant metastasis
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| M1 |
Distant metastasis
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| Stage |
TNM Classification |
| 0 |
Tis (carcinoma in situ) |
| I |
T1 or T2, N0, M0
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| IIA |
T3, N0, M0
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| IIB |
T4, N0, M0
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| IIIA |
T1 or T2, N1, M0
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| IIIB |
T3 or T4, N1, M0
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| IIIC |
Any T, N2, M0
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| IV |
Any T, Any N, M1
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Patients newly diagnosed with colorectal cancer are referred to specialists for treatment. Specialists who treat colorectal cancer include gastroenterologists (doctors who specialize in diseases of the digestive system), colorectal surgeons, medical oncologists, and radiation oncologists (see Finding Your Medical Team). Depending on the stage of the cancer, patients may receive two types of treatment at the same time or one after the other.
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