Diagnosing Types and Stages of Colon Cancer

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Blood vials

If your doctor finds something abnormal on a screening exam, such as a colonoscopy or a virtual colonoscopy, you’ll have follow-up testing to rule out or confirm a colon cancer diagnosis. Your doctor will also order tests to determine what type of colon cancer you have. The most common type is adenocarcinoma.

The other scenario that requires more comprehensive diagnostic testing is when you have symptoms, such as bloody stool, rectal bleeding, abdominal cramping or pain, or changes in bowel habits. This could include diarrhea, constipation, change in consistency of the stool, or narrowing of the stool. Keep in mind that these symptoms may also be present with other colon problems. Diagnostic testing is the only way to know for sure.

If your doctor finds colon cancer, it will be necessary to determine the type and stage of the cancer. The stage gives your doctor information about your prognosis and the best treatment options for you. The stage of colon cancer depends on how deep the tumor extends into the colon wall, whether cancer cells are in lymph nodes, and if the tumor has spread to other organs.

Diagnosing the type and stage of colon cancer may involve the following procedures:

  • Medical history and physical exam

  • Blood tests

  • Colonoscopy

  • Imaging exams

Medical History and Physical Exam

Your medical history is important because it tells your doctor about your risks of colon cancer. This can include information about any chronic diseases, your family medical history, and your lifestyle habits. Your doctor will also want to know about any symptoms you are experiencing. If you are having symptoms, it can be helpful to keep a log of them during the days leading up to your appointment. This will let you communicate accurately with your doctor.

During a physical exam, your doctor will feel your abdomen to check for masses or enlarged organs. Your doctor may also perform a digital rectal exam (DRE). This involves inserting a gloved and lubricated finger into your rectum. Your doctor can feel for tumors or other abnormalities in the rectum, which is the last six inches of the colon.

Blood Tests

Your doctor may order three types of blood tests when diagnosing colon cancer:

  • Complete blood count (CBC) measures the amount of red blood cells, white blood cells, and platelets in your blood. It can also tell your doctor about different features of your red blood cells that indicate whether they are normal or not. For colon cancer, your doctor is looking to see if you are anemic—or have too few red blood cells. This could mean you have a colon tumor that has been slowly bleeding over time.

  • Liver enzymes measure the health of your liver. Metastatic colon cancer most often spreads to the liver and cause problems with these enzymes.

  • Tumor markers detect substances in the blood that tumors release. Common colon cancer tumor markers include CEA and CA 19-9. This test may be part of diagnosing colon cancer, but it is more common for monitoring someone who already has a diagnosis.

None of these tests can be used alone to diagnose colon cancer. If results suggest a problem, your doctor will recommend more tests.


This exam involves inserting a flexible, lighted tube through the anus and into the rectum and large intestine. A camera allows your doctor to view the full length of the interior surface of the large intestine. If your doctor finds a polyp or tumor, he or she can remove it during the colonoscopy. Because colonoscopy is also a common screening exam, this biopsy can take place during the screening procedure. In some cases, surgery may be necessary to take a biopsy.

Your doctor will send the tissue sample to a lab for analysis. The lab will determine whether cancer is present. If so, genetic testing can give your doctor information about the tumor’s characteristics. This can tell your doctor about the best treatment options for you.

If the lab does not find cancer, you may still get information about the polyp, such as precancerous dysplasia. Colon dysplasia represents the appearance of abnormal cellular characteristics when studied under a microscope. Low-grade dysplasia doesn’t look very abnormal. High-grade dysplasia looks more abnormal and may mean you need more frequent follow-up screenings.

Imaging Exams

Imaging exams are useful for staging colon cancer. These exams can show the extent of cancer in the body. There are six imaging exams your doctor may use, including:

  • Angiography is an X-ray test of your blood vessels using a contrast dye. It can identify metastatic tumors in the liver and help your doctor develop a treatment plan.

  • Chest X-ray can locate colon cancer that has spread to the lungs.

  • CT (computed tomography) scan makes detailed images to see if colon cancer has spread to your liver or other organs.

  • MRI (magnetic resonance imaging) also creates detailed images and can help find areas with metastatic colon cancer.

  • PET (positron emission tomography) scan shows areas in the body that take up a radioactive form of sugar in abnormally large amounts. These areas of high metabolism show where cancer has likely spread. Many PET scanners are combination PET/CT machines.

  • Ultrasound can detect metastatic tumors in your liver and other areas in the abdomen. You may also need an endorectal ultrasound to see how far into the colon wall the cancer has grown. This test uses a special instrument that goes into your rectum to make the images.

Your doctor combines the results of these various tests to make a complete diagnosis. Knowing the stage of colon cancer and other information about the tumor helps your doctor create an individualized treatment plan and a path forward. Talk with your doctor to understand how your test results influence your prognosis and your treatment decisions.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Feb 25
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.

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