Colorectal Cancer Diagnosis

  • Diagnosis

    Colorectal cancer is unchecked cell growth in the large intestine (colon) or rectum that results in tumors that can spread to other parts of the body. Figure 01 The colon and rectum make up the end of the 30-foot-long digestive tract. The colon is the 5 feet of muscular tubing near the end that receives digested nutrients from the small intestine and passes non-absorbed waste on to the rectum (the last 8 to 10 inches of the tract), where they are held before they are expelled through the anus.

    Click to enlarge: Colorectal cancer

    Figure 01. Colorectal cancer

    Colorectal cancer can arise anywhere in the colon or rectum. The majority of cases (60%) occur in the lower part of the colon or rectum. A quarter of cancers show up in the rectum. Colorectal cancer tends to develop slowly over many years, and starts out as precancerous lesions or polyps. When detected and treated early enough, colorectal cancer is usually curable. Unfortunately, however, most cases are detected after the cancer has spread, which is why colorectal cancer is the second-leading cancer killer in the U.S.

    Colorectal cancer occurs when abnormal cells in the lining the colon or rectum proliferate out of control. The cancer may originate on the surface of the intestinal lining or on a bud on a stalk that protrudes from the intestinal wall (polyp). Colorectal polyps are very common. As many as 40% of Americans have them by age 50. Most polyps remain noncancerous (benign), but about 5 to 10% go on to become cancerous (malignant) if they are not removed. As the cancer grows, it begins to invade the intestinal wall. Without treatment, it can infiltrate nearby tissues and lymph nodes and spread through the blood to the liver and other organs.

    In its earliest stages, colorectal cancer has few or no symptoms. Therefore, it is extremely important to undergo routine screening tests beginning at age 50. More advanced colorectal cancer can produce changes in bowel habits and bloody stools Table 01. If you experience constipation, diarrhea, or pencil-thin stools for more than 10 days, you should see your doctor. Likewise, blood (bright red or black in appearance) in your stool warrants medical attention, even though it does not necessarily mean that you have cancer. Hemorrhoids or rectal tears might be the culprit. Bowel movements also can become discolored after you eat certain foods, or after you take iron supplements. Abdominal pain, bloating, cramps, and gas are other possible symptoms of colorectal cancer. Loss of appetite and weight loss may occur as well.

    Table 1.   Signs and Symptoms of Colorectal Cancer

    Blood (bright red or black) in stool
    Weight loss
    Appetite loss
    Fatigue
    Cramps, bloating, gas pains
    Diarrhea and/or constipation
    Narrow stools or other changes in bowel habits

    Colorectal cancer can strike men and women of all ages, but occurs most frequently in older adults. The number of colorectal cancer cases begins to rise in people starting around age 40, and peaks after age 70. If you have colorectal cancer in your family, or if you have already had colorectal cancer or have adenomatous polyps (a hereditary condition that results in hundreds of polyps in the colon or rectum), your risk goes up, and the age at which the risk begins is earlier. Other bowel conditions such as ulcerative colitis and Crohn's disease increase the likelihood of colorectal cancer.

    Lifestyle factors such as diet and activity level play a role in colorectal cancer. A diet high in calories and fat—animal fats in particular—may increase colorectal cancer risk; however, this has been questioned. This conclusion comes from the fact that colorectal cancer is not nearly as common in Asia and in other parts of the world where diets tend to be low in animal fat and high in fiber. Colorectal cancer predominantly affects people in affluent Western nations who typically eat less fiber and more animal fat. Race appears to have no influence. Japanese people who live in the U.S. are more likely to get colorectal cancer than those who live in Japan. A lack of exercise and obesity are also associated with higher rates of colorectal cancer.

    A fecal occult blood test (FOBT) can reveal blood that may be hidden in your stool—one of the earliest signs of colorectal cancer. FOBTs are easy to do, and are noninvasive. One common method involves analyzing samples from three consecutive bowel movements. You collect the samples at home, and bring them to your doctor or mail them directly to a laboratory. It is best to use test kits supplied by your doctor rather than ones purchased over-the-counter. The latter are not as reliable.

    Doing an FOBT involves placing a bit of stool on a chemically treated paper that changes color after development when blood is present. A positive finding does not mean you have cancer—you may have hemorrhoids or an infection. If you take aspirin or other NSAIDs, this could produce a positive result as well. Likewise, eating certain foods (rare beef, raw broccoli, bean sprouts, cauliflower, oranges, apples, bananas) could be confounding the results. Also, iron supplements may lead to a misreading of the test as falsely positive.

    A positive FOBT warrants a more thorough investigation of your colon and rectum. Sigmoidoscopy, colonoscopy, barium enemas, and digital rectal exams are tools that may be used. Sigmoidoscopy and colonoscopy use a flexible, lighted viewing tube (endoscope) inserted through the anus that enables careful inspection of the colon. Sigmoidoscopy only permits examination of the lower two feet of the colon only, whereas colonoscopy offers a complete view of the colon and the rectum. About 70% of colorectal cancers occur in areas that can be seen during sigmoidoscopy. Both procedures can be done on an outpatient basis. A sedative can minimize discomfort during a colonoscopy, the more involved of the two tests.

    Before a sigmoidoscopy or colonoscopy, you will be asked to consume a liquid diet and take a laxative, or have an enema to empty your bowel. If your doctor finds suspicious lesions, he or she will take a sample for analysis. If polyps are detected during a colonoscopy, they will likely be removed at this time.

    Because a sigmoidoscopy does not provide a complete picture of the colon, it should be accompanied by a barium enema with air contrast study of the upper colon and a digital rectal exam (DRE). Barium is a chalky white substance that can reveal colon abnormalities on an x-ray. For such a test, you will be given a barium enema followed by air to expand your colon, and then x-rays will be taken. Your doctor can feel for rectal abnormalities during a DRE, which involves inserting a gloved, lubricated finger into the anus. DREs are usually done as part of routine pelvic exams for women and prostate checks for men. Unfortunately, a substantial proportion of small to medium-sized polyps, and some cancers, will be missed on a barium enema.

    Virtual CT colonoscopy is an experimental test that is less invasive than a traditional colonoscopy. It involves an enema followed by air to expand the colon, followed by a CT scan. Computer images provide three-dimensional views of the colon. This technique is more comfortable than a regular colonoscopy, but may not be as effective for detecting cancer because the doctor is unable to take biopsies. As more experience is gained with this test, it may become an alternative to a first-step screening test. At present, relatively few centers have experience with this, and the test remains insensitive for small polyps or cancers.

    If cancer is found, your doctor will determine its grade and stage to help guide decisions regarding your treatment Grade and stage indicate how aggressive your cancer is and whether/how far it has spread. This information is essential for plotting an appropriate treatment plan, which will involve surgery, radiation therapy, chemotherapy, or a combination of these approaches.

    A biopsy of the lesion can reveal the grade—how “aggressive” or how different the cells look compared with normal cells. The stage will fall between 0 and 4, depending on the extent of cancer spread within the intestinal wall, whether cancer has invaded neighboring tissues, and whether cancer has spread to the lymph nodes, liver, lungs, or elsewhere in the body. A stage 0 cancer has not yet become invasive; a stage 4 cancer has spread to the liver or some other non-colonic site.

    Regular screening can detect colorectal polyps and cancer very early on—before symptoms are apparent, and when cancer can be prevented or cured. Colorectal cancer frequently begins as polyps. Not all polyps turn cancerous, but there is no way to tell which ones will and which ones will not. Therefore, if growths are found, it is best to have them removed, which is usually done at colonoscopy. Colorectal cancer is more than 90% curable when found and treated early, but less than a third of Americans follow the screening protocol necessary for this to happen. Although risk factors are important for determining which type of tests should be administered and how often they should be done, 70% to 80% of colorectal cancers are found in people of average risk. This is why the American Cancer Society (ACS) recommends that all Americans undergo a yearly DRE beginning at age 40. At age 50, annual FOBTs and a sigmoidoscopy every 5 years are advised. The ACS also recommends a colonoscopy every 10 years or a double-contrast barium enema every 5 for people in this age group, although this more aggressive approach is usually reserved for higher risk individuals. Screening should be done earlier and more frequently if you have risk factors for colorectal cancer. Having colorectal polyps, ulcerative colitis, Crohn's disease, or a personal or family history of colorectal cancer puts you at increased risk. A family history of breast or endometrial cancer also slightly elevates your risk.

    Following a healthy diet and exercise regimen may help lower your risk for colorectal cancer. Aim for a low-fat, high-fiber diet. Try to get at least five servings of fruits and vegetables and six servings of other plant-based foods such as cereals, breads, rice, pasta, and beans every day. Keep red meat and other foods containing animal fat to a minimum. Some research suggests that taking a multivitamin that has folic acid lowers colorectal cancer risk. Other studies have found that boosting calcium intake through supplements or low-fat dairy products could also lower risk.

    It is also important to achieve and maintain a healthy weight. Research shows that excess fat can alter metabolism in such a way that increases the growth rate of cells in the colon and rectum. A moderate exercise regimen—half an hour of physical activity most days of the week—can help you keep your weight under control. These dietary recommendations are best followed on a lifelong basis. Altering one's diet after the appearance of colonic polyps has very little effect on limiting future polyp occurrence.

    Taking aspirin and other NSAIDs seems to play a role in preventing colorectal cancer. Several population studies have consistently found that people who take aspirin on a regular basis are at much lower risk for acquiring colorectal cancer and pre-cancerous polyps. However, clinical trials have not explored this issue, nor has an appropriate preventative dose been determined.

  • Prevention and Screening

    Regular screening can detect colorectal polyps and cancer very early on—before symptoms are apparent, and when cancer can be prevented or cured. Colorectal cancer frequently begins as polyps. Not all polyps turn cancerous, but there is no way to tell which ones will and which ones will not. Therefore, if growths are found, it is best to have them removed, which is usually done at colonoscopy. Colorectal cancer is more than 90% curable when found and treated early, but less than a third of Americans follow the screening protocol necessary for this to happen. Although risk factors are important for determining which type of tests should be administered and how often they should be done, 70% to 80% of colorectal cancers are found in people of average risk. This is why the American Cancer Society (ACS) recommends that all Americans undergo a yearly DRE beginning at age 40. At age 50, annual FOBTs and a sigmoidoscopy every 5 years are advised. The ACS also recommends a colonoscopy every 10 years or a double-contrast barium enema every 5 for people in this age group, although this more aggressive approach is usually reserved for higher risk individuals. Screening should be done earlier and more frequently if you have risk factors for colorectal cancer. Having colorectal polyps, ulcerative colitis, Crohn's disease, or a personal or family history of colorectal cancer puts you at increased risk. A family history of breast or endometrial cancer also slightly elevates your risk.

    Following a healthy diet and exercise regimen may help lower your risk for colorectal cancer. Aim for a low-fat, high-fiber diet. Try to get at least five servings of fruits and vegetables and six servings of other plant-based foods such as cereals, breads, rice, pasta, and beans every day. Keep red meat and other foods containing animal fat to a minimum. Some research suggests that taking a multivitamin that has folic acid lowers colorectal cancer risk. Other studies have found that boosting calcium intake through supplements or low-fat dairy products could also lower risk.

    It is also important to achieve and maintain a healthy weight. Research shows that excess fat can alter metabolism in such a way that increases the growth rate of cells in the colon and rectum. A moderate exercise regimen—half an hour of physical activity most days of the week—can help you keep your weight under control. These dietary recommendations are best followed on a lifelong basis. Altering one's diet after the appearance of colonic polyps has very little effect on limiting future polyp occurrence.

    Taking aspirin and other NSAIDs seems to play a role in preventing colorectal cancer. Several population studies have consistently found that people who take aspirin on a regular basis are at much lower risk for acquiring colorectal cancer and pre-cancerous polyps. However, clinical trials have not explored this issue, nor has an appropriate preventative dose been determined.

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