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Diagnosing Colorectal Cancer

To make a diagnosis, your doctor will likely have you undergo the following exams:

Physical Exam: During the exam, your doctor will look for tenderness, swelling, or unusual growths that might be felt in your rectum or the lower part of your colon. Your doctor will also check the rest of your body to look for signs of spread to other sites and to evaluate your overall health.

Colonoscopy: If you had a positive fecal occult blood test or a sigmoidoscopy (a test that looks at the lower colon and anus), your doctor will want to evaluate your full colon, which will require a colonoscopy. During the colonoscopy, biopsies of the tumor and any other suspicious tissue can be taken and sent to a pathologist for evaluation under a microscope.

Blood Tests: A complete blood count (CBC) will help your doctor get a picture of your overall health. Many people with colorectal cancer lose blood in the stool, even if they cannot see it. The CBC will also provide information about your doctor red blood cell count. If it is low, you may be anemic.

Your doctor will also probably request a CEA (Carcinoembryonic Antigen) test. CEA is a tumor marker that can be detected in the blood. CEA is not always high in patients with colorectal cancer and it can be elevated for other reasons. For some people, CEA is a good marker that can help your doctor monitor your status during and after treatment. CEA should be measured before any treatment, including surgery. Your doctor may also request a CA 19-9 test. CA 19-9 is a blood marker that may be elevated in colorectal cancer.

Imaging Studies: These tests allow your doctor to see if the cancer has spread to other parts of the body. You may have a CT scan of your chest, abdomen and pelvis. Your doctor may also request MRI scans. These provide additional information about areas of the body where the cancer may have spread. If you have rectal cancer, you may have an ultrasound test, which uses sound waves to create an image. Chest X-rays and PET scans are not routinely used to image colorectal cancer but your doctor may request them if they want to get more information about a potential site of metastases.

Tumor Tissue Testing: Your doctor may request that specific tests be performed on the tumor tissue. These genetic tests are done on a sample of the tumor tissue removed during the biopsy or during surgery and provide information about the specific mutations in your tumor. Your doctors will use this information to determine which treatments will be best for you or if your tumor may be associated with an inherited cancer syndrome. These tests include:

  • KRAS Mutation Test: This test is done in patients with stage IV metastatic colorectal cancer. It looks for a mutation in the KRAS gene that is commonly found in colorectal cancer. Knowing whether your tumor has the KRAS mutation is important because it provides information about how your tumor should be treated. Tumors that do not have the mutation will not respond to a type of drug called an EGFR-inhibitor.If your tumor does have the mutation, your doctor is likely to recommend that you are treated with an EGFR inhibitor, such as cetuximab (Erbitux) or (Vectibix).
  • Oncotype DX Colon Cancer Assay: If you have stage II or stage III colorectal cancer, your doctor may recommend your tumor be tested the Oncotype DX colon cancer test. This test analyzes 12 different genes, producing a score zero and 100. The score is an estimate of your risk of having your cancer recur after surgery. A low score means you have a low risk of recurrence, and a high score means your risk of recurrence is high. The result may help you and your doctor determine if you will benefit from chemotherapy.

Your final diagnosis and cancer stage may not be known until after you have surgery. During the surgery, the surgeon will remove not just the tumor itself, but also tissue around the tumor (called margins) and fat and lymph nodes attached to the area where the tumor was found. A pathologist will look at the tissue that was removed during surgery to help determine the stage of the cancer.

If colorectal cancer is diagnosed, the doctor needs to know the stage, or extent, of the disease to plan the best treatment. Staging is a careful attempt to find out whether the cancer has spread, and if so, to what parts of the body.