To understand colorectal cancer, it is first helpful to understand what parts of the body are affected and how they work.
The colon
The colon is an approximately 5 to 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 so that emptying the bowels is easy and convenient. Once or twice a day the colon empties its contents into the rectum to begin the process of elimination.
The rectum
The rectum is a 5- to 6-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let you know that there is stool to be evacuated, and to hold the stool until defecation occurs.
What is colorectal cancer?
Cancer that begins in the colon is called colon cancer, while cancer that begins in the rectum is known as rectal cancer. Cancers affecting either of these organs also may be referred to as a colorectal cancer. Colorectal cancers generally arise over time from adenomatous (precancerous) polyps after a series of mutations in their cellular DNA. The exact cause of colorectal cancer is not known. Some of the risk factors for colorectal cancer involve heredity, diet, alcohol intake, smoking, and inflammatory bowel disease.
What are the signs and symptoms of colorectal cancer?
Unfortunately, colorectal cancer might strike without any signs or symptoms. For this reason, it is very important to have regular examinations, called colorectal screenings, to detect problems early. The best screening evaluation is a colonoscopy; other screening modalities include a flexible sigmoidoscopy, barium enema, and CT colonography (virtual colonoscopy).
However, not all colorectal cancers are without signs or symptoms. One of the early signs of colorectal cancer might be 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. When tumors have grown larger, other signs and symptoms might develop. These include:
- Change in bowel habits — Constipation, diarrhea, narrowing of stools, incomplete evacuation, and bowel incontinence -- although usually symptoms of other, less serious problems -- can also be symptoms of colorectal cancer.
- Blood on or in the stool — By far the most noticeable of all the signs, blood on or in the stool can be associated with colorectal cancer. However, it does not necessarily indicate cancer, since numerous other problems can cause bleeding in the digestive tract, including hemorrhoids, anal tears (fissures), ulcerative colitis, and Crohn’s disease, to name only a few. In addition, iron and some foods, such as beets, can give the stool a black or red appearance, falsely indicating blood in the stool. However, if you notice blood in or on your stool, see your doctor to rule out a serious condition and to ensure that proper treatment is received.
- Unexplained anemia — Anemia is a shortage of red blood cells, the sort that carry oxygen throughout the body. If you are anemic, you may experience shortness of breath. You may also feel tired and sluggish, so much so that rest does not make you feel better.
- Unusual abdominal pain or bloating
- Unexplained weight loss
- Vomiting
If you experience any of these signs or symptoms, it is important to see your doctor for evaluation. For a patient with colorectal cancer, early diagnosis and treatment can be life-saving.
What are the stages of colorectal cancer?
Colorectal cancer is described clinically by the stages in 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. 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 colorectal cancers, 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, is all that is required.
Stage 1. Stage 1 colorectal cancers have grown through several layers of the intestine but have not spread beyond the muscular coat of the colon or rectum. The standard treatment of a stage I colon cancer is a colon resection alone. The type of surgery used to treat a rectal cancer is dependant upon its location, but includes a low anterior resection or an abdominoperineal resection.
Stage 2. A stage 2 colorectal cancer has penetrated beyond the muscular layers of the large intestine (stage 2A) and even spread into adjacent tissue (stage 2B). However, it has not yet reached the lymph nodes. Usually the only treatment for this stage of colon cancer is a surgical resection. Since some stage 2 colon cancers have a tendency to recur, the doctor may also decide to treat the patient with chemotherapy after surgery. For a stage 2 rectal cancer, a surgical resection is sometimes preceded or followed by chemotherapy and radiation.
Stage 3. A stage 3 colorectal cancer is considered an advanced stage of cancer as the disease has spread to the lymph nodes, but not to other parts or organs in the body. For a colon cancer, surgery is 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 aimed at 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 or, in the case of minimal disease in the liver, treated with radiofrequency ablation (destruction by a painless energy wave source), 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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