Detecting and Diagnosing Colorectal Cancer


Many tests are used by doctors to detect, diagnose, and stage colorectal cancer. Tests are also used to see if cancer has spread (metastasized) to other parts of the body from where it started.

Like many cancers, colon and rectal cancers don’t usually show obvious symptoms in the beginning. The good news is that understanding your family history and talking with your doctor about regular colorectal screening can increase the chance of treating it successfully.

Common Types of Screening for Colon and Rectal Cancers

There are several screening options to choose from, ranging from tests that can be conducted at home to ones that are performed at a healthcare facility. Although at-home testing offers more privacy, it’s important to understand that they can often lead to a false positive or a misinterpretation of the results.

In general, the best method of screening depends on factors such as your age and risk for developing colon and rectal cancer. Talking with your doctor can help when it comes to making a decision on a screening test.

At-Home Testing for Colorectal Cancer

If you're under the age of 50, your doctor may suggest at-home testing before a colonoscopy or other test performed by a healthcare professional. This allows you to do the test in the comfort of your home without a day of colon preparation before a colonoscopy. Although convenient, these tests can miss many polyps and some cancers.

Stool DNA Test

A stool DNA test could be an option for those who would prefer to avoid the preparation and invasive testing of a colonoscopy. Simply get the take-home test kit from your doctor, collect a stool sample, and mail it to the lab. The test checks for blood in the stool and gene changes.

Although stool DNA tests are convenient and non-invasive, they are not for everyone. This type of testing should be reserved for only those with an average risk for colon or rectal cancer. If the test results are abnormal, additional testing through colonoscopy may be needed.

Guaiac-based Fecal Occult Blood Test (gFBOT)

The guaiac-based fecal occult blood test (gFBOT) checks the stool for blood that can only be seen under a microscope. After you collect a stool sample onto a test card, you will return the card back to the doctor’s office for testing.

gFBOT uses a chemical to detect heme, a component of the blood protein hemoglobin. Since this test may detect heme in certain foods and medications, such as red meat, you will most likely be required to eat a special diet prior to screening.

Fecal Immunochemical Test (FIT)

A fecal immunochemical test (FIT) is very similar to the gFBOT, and it uses antibodies to specifically detect human hemoglobin protein. However, unlike the gFBOT, there are no dietary restrictions prior to testing.

Colorectal Cancer Screening Performed at a Healthcare Facility

The following tests are ones that are conducted by a healthcare facility. Your doctor can help you determine which test is the best one for you.

Standard Colonoscopy

This test involves the use of a flexible lighted tube called a colonoscope. Inserted into the rectum, the colonoscope features a lens for viewing and a tool for removing tissue. Air is inserted into the rectum, helping doctors to better view the colon lining. If found, abnormal growths can be removed for testing during this procedure.

A thorough cleansing of your colon prior to testing as well as being sedated during the test are two important steps that help contribute to a successful colonoscopy. According to the National Cancer Institute, studies show that colonoscopy screening can reduce colorectal cancer deaths as much as 60-70%. Because of this, colonoscopy is often the preferred screening test for early detection. A key benefit of a colonoscopy is the ability to view the entire colon.

Virtual Colonoscopy

With this test, a CT scanner takes images of the colon. This test typically does not require sedation, however, it does require bowel preparation. During the test, air is pumped into your colon and rectum, which makes it possible for the scanner to show detailed, cross-sectional images. If the doctor sees polyps or possible cancer, a standard colonoscopy may be ordered for confirmation.

Patients aged 50 and over and who are considered to have an average risk for colon cancer are ideal candidates for a virtual colonoscopy. A doctor may also order a virtual colonoscopy if there is a bowel obstruction or you are at risk for complications from a regular colonoscopy.

Flexible Sigmoidoscopy

Similar to a colonoscopy, this test looks only at part of the colon. In most cases, there is no need for sedation during a flexible sigmoidoscopy test. Doctors can either remove polyps during the test or order a colonoscopy. Although bowel preparation is necessary, it is not as extensive as that required for a colonoscopy.

When to Get Screened for Colorectal Cancer

Current research has found that younger adults are being affected by colorectal cancer. Because of this, the American Cancer Society (ACS) now recommends colon and rectal cancer screening begin at age 45 rather than 50. Research remains ongoing, however, several contributing factors attributed to the increase are poor diets, lack of physical activity, and obesity.

Screening recommendations for colon and rectal cancer differ based upon whether a patient is at average risk or high risk for the disease. Patients who are at average risk tend to have no family history of colorectal cancer and are, on average, fairly healthy. The ACS recommends average-risk patients undergo a thorough screening every ten years.

Patients considered high risk for colorectal cancer likely have one or more of the contributing factors:

  • A family history of colon or rectal cancer

  • Problems with inflammatory disease

  • Radiation to the pelvic area from a previous cancer

The ACS recommends that high-risk patients begin screening earlier than age 45 and scheduling screenings more frequently than every 10 years. Prevention is key and especially important for those at high risk of developing colon or rectal cancer.

When Test Results Come Back Abnormal

Further testing is often required before a doctor can diagnose colon or rectal cancer. When any test other than a colonoscopy indicates abnormalities, a doctor may order a colonoscopy in order to view the colon in its entirety.

If pathology testing of polyps removed during a colonoscopy returns a cancer diagnosis, your doctor will work to stage the cancer. Discovering whether the cancer has spread helps a doctor to determine the stage.

It is important to remember that not all polyps are cancer. Before jumping to conclusions, wait to hear from your doctor.

Colorectal Cancer Signs & Symptoms

In many cases, symptoms of colorectal cancer don’t usually present themselves until the cancer has become more advanced. Because of this, it’s important to familiarize yourself with the early warning signs of colon and rectal cancer and talk with your doctor about getting screened. The sooner colorectal cancer is caught, the more easily treatable it will be.

In most cases, colorectal cancer begins as small, noncancerous (benign) clumps of cells called adenomatous polyps, which over time, can develop into cancer. This can lead to symptoms such as:

  • Changes in bowel habits, such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days

  • Rectal bleeding or blood in your stool

  • Stool that is dark in color

  • Unexplained weight loss

  • Fatigue or weakness

  • A feeling of not being able to empty your bowels

  • Abdominal discomfort (i.e. bloating, gas, or cramps)

When to Visit the Doctor

It’s important to remember that these symptoms don’t always mean cancer. Sometimes, they are the result of something else entirely, such as an infection, hemorrhoids, irritable bowel syndrome (IBS), or inflammatory bowel disease (IBD). Still, the appearance of any symptoms like the ones listed above, or, anything that seems out of the ordinary, should be brought to the attention of your primary care physician so your condition can be properly assessed.

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