Diagnosing Colon & Rectal Cancer

As with most other cancers, colorectal cancer doesn’t always come with obvious signs and symptoms until the disease has spread to a more advanced stage. This is why it’s important to understand your family history and talk with your primary care physician about scheduling regular colorectal cancer screening. 

What is the age for colonoscopy? Even if you’re feeling fine, Minnesota Oncology recommends that you follow the guidelines set in place by the American Society of Clinical Oncology, to get a colonoscopy starting at age 45. 

Common Types of Screening for Colon and Rectal Cancers

Fortunately, there are several screening tests for colon and rectal cancers, including some that were recently made widely available. In addition to detecting colorectal cancer when it is present, regular screening can also prevent it by allowing your doctor to find and remove polyps before they have a chance to turn into cancer. To stay on top of your health, we recommend you take time to schedule an appointment with your primary care physician so you can learn more about your colon cancer screening options. 

There are several common types of screening options. These tests range from those that are performed at a healthcare facility to those that can be conducted at home. Keep in mind that even though at-home testing offers more privacy, they are more prone to producing a false positive or a misinterpretation of the results.

Common colorectal cancer screening tests (colon cancer detection tests) include: 

  • Virtual colonoscopy. This screening method, also called computed tomographic (CT) colonography, uses special x-ray equipment (a CT scanner) to produce a series of pictures of the colon and the rectum from outside the body.
  • Sigmoidoscopy. In this test, the rectum and lower (sigmoid) colon are examined using a sigmoidoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue. The doctor cannot check the upper part of the colon, the ascending and transverse colon, with this test. 
  • Standard (or optical) colonoscopy. In this test, the rectum and entire colon are examined using a colonoscope, a flexible lighted tube with a lens for viewing and a tool for removing tissue.
  • Double-contrast barium enema (DCBE). An enema can be given containing barium. Once the barium has moved into the colon, x-rays are taken. The images are used to detect areas where there may be cancer. It’s not a good option for identifying precancerous polyps, but is better than nothing if a colonoscopy or other physical exam isn’t possible. 
  • Fecal Occult (Hidden) Blood Tests (FOBT) - There are two types of tests that can be done at home to test for very small amounts of blood in the stool that may be the result of a polyp or cancerous tumor that has been irritated, but does not cause enough bleeding to be detected during a bowel movement. One problem with FOBTs is that the doctor can’t tell if the blood that’s detected is from within the colon or rectum. If there is blood found, a colonoscopy is usually the next step to see if the source of the blood is from within the colon. 
  • Fecal Immunochemical Test (FIT).This test looks for hidden blood in the stool by reacting to part of the human hemoglobin protein, which is found in red blood cells.
  • Guaiac-based fecal occult blood test (gFOBT). This is similar to the FIT, but with a different type of chemical reaction used to detect the presence of blood in the stool.
  • Stool DNA test. A test that detects tiny amounts of blood in stool (with an immunochemical test similar to FIT) as well as nine DNA biomarkers in three genes that have been found in colorectal cancer and precancerous advanced adenomas. This test can be conducted at home. 

The best method of screening depends on factors such as your age and risk for developing colon and rectal cancer.

Screening Recommendations for Colorectal Cancer

Screening recommendations for colon and rectal cancer differ based upon whether a patient is at average risk or high risk for the disease. The American Society of Clinical Oncology has developed guidelines for patients who are at average risk tend to have no family history of colorectal cancer and are, on average, fairly healthy. The beginning age for colonoscopy for both men and women is 45.

Every year starting at age 45 perform a Fecal Occult Blood Test (FOBT) at home to detect signs of blood in the colon. This would be either the FIT or the Guaiac-based FOBT. A DNA Stool test would only be performed when directed by your physician.  You may not need to have an actual colonoscopy or other internal exam every year as long as you and your doctor have a plan for screening in other ways in between.

Here is a recommendation from ASCO based for physical exams in addition to annual FOBTs.

  • Flexible sigmoidoscopy, every 5 years or every 10 years with FIT or FOBT every year
  • Colonoscopy, every 10 years
  • Double-contrast barium enema (DCBE), every 5 years
  • Virtual colonoscopy, as often as your doctor recommends

If you are considered at high risk for colorectal cancer, your doctor may recommend earlier and more frequent screening. The following factors could increase your risk of colorectal cancer: 

  • A family history of colon or rectal cancer
  • Problems with inflammatory disease 
  • Radiation to the pelvic area from a previous cancer

Talk with your doctor if you feel as though you may fall into the high-risk category. 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.

The following tests may be used to diagnose colorectal cancer :

  • Blood tests: Your doctor checks for carcinoembryonic antigen (CEA) and other substances in the blood. Some people who have colorectal cancer or other conditions have a high CEA level.
  • Colonoscopy: If colonoscopy was not performed for diagnosis, your doctor checks for abnormal areas along the entire length of the colon and rectum with a colonoscope.
  • Endorectal ultrasound: An ultrasound probe is inserted into your rectum. The probe sends out sound waves that people cannot hear. The waves bounce off your rectum and nearby tissues, and a computer uses the echoes to create a picture. The picture may show how deep a rectal tumor has grown or whether the cancer has spread to lymph nodes or other nearby tissues.
  • PET-CT scan: A PET scan uses small amounts of radioactive materials, a special camera, and a computer to create pictures of organs and tissues inside the body. When a PET scan is combined with a CT scan, it is usually called a PET-CT scan. 
  • MRI: The use of magnetic fields, not x-rays, to produce detailed images of the body. You may receive an injection of dye, called a contrast medium, to create a clearer picture. MRI is the best imaging test to find where the colorectal cancer has grown.
  • CT scan: An X-ray machine linked to a computer takes a series of detailed pictures of areas inside your body. You may receive an injection of dye. A CT scan may show whether cancer has spread to the liver, lungs, or other organs.
  • Chest X-ray: X-rays of your chest may show whether cancer has spread to your lungs.

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. Sometimes staging is not complete until after surgery to remove the tumor (see the treatment section for surgery information).  

You can read more about staging on our Colon & Rectal Cancer Staging page.

It is important to remember that not all polyps are cancerous. It is always best to hear from your doctor before jumping to conclusions. 

Minnesota Oncology is Here to Help

It is important to stay on top of your colorectal screening with your primary care physician. At Minnesota Oncology, our highly experienced oncology professionals are standing by to help treat colorectal cancer with a treatment plan designed specifically for you.  

In addition to paying attention to symptoms and understanding more about your family history, talking to your doctor about getting screened for colorectal cancer is arguably the most effective way you can reduce your risk.