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Colorectal Cancer: Symptoms and Diagnosis

Jessica Evert, MD, edited by Benjamin McDonald, MD

list with boxes checkedEarly and middle stage colorectal cancers often present with few or no observable symptoms, making them difficult to identify without the benefit of a doctor's screening tests (described below). When symptoms are apparent, they tend to take the following forms:

  • Changed bathroom habits that do not resolve within a week (including diarrhea, constipation or any obstruction of the colon)
  • Bloody stool (note that stool blood is generally not visible or obvious). Blood in stool often presents as black, tarry stool. If you notice your stools are darker or tar-like, bring this to the attention of your doctor.
  • Thinner than normal or otherwise malformed stools
  • Pain in the lower abdomen
  • Anemia that cannot be accounted for by other conditions (such as menstruation)
  • Weight loss that cannot be accounted for by other conditions

As with many cancers, the outlook (prognosis) for patients with colorectal cancer is better when the disease is identified earlier in its progression rather than later. The earlier the cancer is found the greater the likelihood it can be successfully treated and cured. Individuals who are at risk for colorectal cancer should receive regular professional medical screenings to identify any problem at the earliest possible opportunity.

Medical screening for colorectal cancer frequently involves one or more of the procedures described below. Because these methods involve procedures such as stool sampling and rectal insertion (to check for polyps), they are sometimes perceived as embarrassing, shameful, or painful. On these grounds, some people who might otherwise benefit from screening tests may instead avoid them. It is important to keep in mind that the actual discomfort involved in the screening process is minimal, and that the entire screening process is private between the doctor and patient. Rationally considered, the benefits of colorectal screening far outweigh reasons for avoiding the process. Finding a physician with whom you feel comfortable may be the key needed to combat any feelings of embarrassment.

The U.S. Preventive Services Task Force recommends that annual colorectal screenings start at age 50 and continue until age 75. After age 75, it should be an individual decision with one's doctor, taking into account overall health and potential cancer risk. There are different combinations of screening protocols that are recommended, each with its own timetable for how often it needs to occur. Screening protocols include the following:

US Guidelines 2018

Regardless of which protocol you follow any positive test results should be followed up with a full colonoscopy so that further detail can be detected. Here are descriptions of these screening tests:

Fecal Occult Blood Test (FOBT). This test looks for blood within a sample of your stool. Generally, you take your own sample, and deposit bits of it onto a card provided as part of a take-home kit provided to you for this purpose. The card is then submitted to a laboratory, which then conducts the analysis. A positive finding means that something in your GI track (from your mouth to your anus) is bleeding and merits further investigation. The test is non-specific, however, because any number of conditions, some potentially dangerous (such as polyps and/or tumors) and some benign (like hemorrhoids) might have caused the bleeding. Also, many colorectal cancers do not bleed, or bleed only intermittently. For these reasons, it is common to complement the fecal blood test with additional tests.

Digital Rectum Exam with Fecal Immunochemical Test (FIT). During this test a doctor inserts gloved and lubricated fingers into your anus. The doctor then evaluates a small sample of stool for blood. In men, this exam is also used to check the prostate. In women, it is used to evaluate the space between the rectum and uterus. This test is minimally invasive (as invasive tests go) and causes little or no discomfort. This is only a screening test and is not specific for colorectal cancer. Doctors may also use this exam to see if a patient has internal or external hemorrhoids. This test is preferred over the FOBT. Persons over 50 should get a digital rectal exam with FIT once a year.

Barium Enema. The barium enema test is a method of imaging the structure of your colon. Radioactive barium dye is placed into your colon by means of an enema, and then an x-ray picture of your colon is taken. The barium dye highlights the colon structure and surfaces in a way that would not be possible if the dye were not used. The enema method of inserting the dye into the colon can cause some temporary discomfort. Doctors examine the x-ray pictures resulting from this procedure for polyps and other signs of cancer. This test is not as good at detecting cancer as colonoscopy and has fallen out of favor in recent years.

Virtual Colonoscopy. Virtual colonoscopy involves the use of sophisticated medical imaging procedures such as computed tomography (also known as a CT or CAT scan) and magnetic resonance imaging (known as MRI) to produce a detailed picture of the soft tissues making up the colon and rectum. Virtual colonoscopy is fast, minimally invasive, and produces better images than the older barium enema technique, but it does not resolve fine details or small polyps nearly as well as an actual colonoscopy (described below). Further, if the images suggest that a problem may exist, regular colonoscopy will still be necessary in order to get tissue samples for testing. As virtual colonoscopy technology is newer and more 'hi-tech' than older imaging techniques it can be more expensive as well.

Flexible Sigmoidoscopy. During this procedure a doctor inserts a small flexible tube containing a light and a camera (an endoscope or colonoscope) into your rectum. The doctor moves the tube through the lower sections of your colon to look for polyps or other signs of colorectal cancer. The endoscope blows air into your colon to inflate it so as to properly visualize the tissues. This test, which may cause minor discomfort, commonly takes only a few minutes to perform. Sedation is generally administered. In some cases, doctors will use flexible sigmoidoscopy in conjunction with the barium enema test to find small polyps that the x-ray images would not otherwise resolve. If polyps or similar abnormal tissues are found, the doctor can use the endoscope to take a sample of that tissue for later analysis. The American Cancer Society recommends that people 50 years old or older have a sigmoidoscopy or similar procedure performed every five years.

Colonoscopy. Colonoscopy (not to be confused with virtual colonoscopy) is very similar in principle to flexible sigmoidoscopy. The major difference is that colonoscopy is far more thorough, involving visualization of the entire colon (rather than just the lower half as in sigmoidoscopy). Colonoscopy is the best test available for discovering signs of colorectal cancer, but also one of the more expensive tests that can be conducted. The American Cancer Society recommends that people 50 years old or older have a colonoscopy every ten years. One benefit of a colonoscopy is that they can be both diagnostic and therapeutic (used to treat any concerning polyps).