To understand colorectal cancer, it is first helpful to understand what parts of the body are affected and how they work.
The colon is an approximately 150 - 180 centimeter (5 - 6 foot) long tube that connects the small intestine to the rectum. The colon—which, along with the rectum, is called the large intestine—is a highly specialized organ that is responsible for processing and storing waste. The colon periodically empties its contents—stool—into the rectum to begin the process of elimination.
The rectum is a 12.5 - 15 centimeter (5 - 6 inch) chamber that connects the colon to the anus. It is the job of the rectum to hold the stool until defecation (evacuation) occurs.
Cancer that begins in the colon is called a colon cancer, while cancer in the rectum is known as a rectal cancer. Cancers affecting either of these organs also may be referred to as a colorectal cancer. Colorectal cancers generally develop over time from adenomatous (precancerous) polyps—growths—after a series of mutations (abnormalities) arise in their cellular DNA. The exact cause of colorectal cancer is not known. Some of the risk factors for colorectal cancer involve a family history of colon or rectal cancer, diet, alcohol intake, smoking, and inflammatory bowel disease.
Unfortunately, some colorectal cancers might be present without any signs or symptoms. For this reason, it is very important to have regular colorectal screenings (examinations) to detect problems early. The best screening evaluation is a colonoscopy. Other screening modalities include fecal occult blood tests, flexible sigmoidoscopy, barium enema, and CT colonography (virtual colonoscopy). The age at which such screening tests begin depends upon your risk factors, especially a family history of colon and rectal cancers.
However, most colorectal cancers are associated with signs or symptoms. One of the early signs of colorectal cancer is bleeding. However, tumors often bleed only small amounts, off and on, so that evidence of the blood is found only during chemical testing of the stool, which is called a fecal occult blood test. Other signs and symptoms include:
Colorectal cancer is described clinically by the stages at which it is discovered. The various stages of a colorectal cancer are determined by the depth of invasion through the wall of the intestine; the involvement of the lymph nodes (the drainage nodules); and the spread to other organs (metastases). Listed below is a description of the stages of colorectal cancer and their treatment. In most cases, treatment requires surgical removal (resection) of the affected part of the intestine. For some tumors, chemotherapy or—for rectal cancers—radiation are added to manage the disease.
Stage 0. For cancers that are stage 0—also known as carcinoma in situ—the disease remains within the lining of the colon or rectum. Therefore, removal of the cancer, either by polypectomy via colonoscopy or by surgery if the lesion is too large, may be all that is required for treatment.
Stage 1. Stage 1 colorectal cancers have grown into the wall of the intestine but have not spread beyond its muscular coat. The standard treatment of a stage I colon cancer is usually a colon resection alone, in which the affected part of the colon and its lymph nodes are removed. The type of surgery used to treat a rectal cancer is dependent upon its location, but includes a low anterior resection or an abdominoperineal resection, which are described in other patient information forms.
Stage 2. A stage 2 colorectal cancer has penetrated beyond the muscular layers of the large intestine (stage 2B) and even spread into adjacent tissue (stage 2C). However, it has not yet reached the lymph nodes. Usually the only treatment for this stage of colon cancer is a surgical resection, although chemotherapy after surgery may be added. For a stage 2 rectal cancer, a surgical resection is sometimes preceded or followed by chemotherapy and/ or radiation.
Stage 3. A stage 3 colorectal cancer is considered an advanced stage of cancer as the disease has spread to the lymph nodes. For a colon cancer, surgery is usually done first, followed by chemotherapy. Chemotherapy and radiation may precede or follow surgery for a stage 3 rectal cancer.
Stage 4. For patients with stage 4 colorectal cancer, the disease has spread (metastasized) to distant organs such as the liver, lungs, or ovaries. When the cancer has reached this stage, surgery is generally used for relieving or preventing complications as opposed to curing the patient of the disease. Occasionally the cancer’s spread is restricted enough to where it can all be removed by surgery. In the case of minimal disease in the liver, the tumor may be treated with radiofrequency ablation (destruction with heat), cryotherapy (destruction by freezing), or intra-arterial chemotherapy. For stage 4 cancer that cannot be surgically removed, chemotherapy, radiation therapy, or both may be used to relieve, delay, or prevent symptoms.
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