Colorectal Cancer: Diagnosis

How is colorectal cancer diagnosed?

Your healthcare provider might believe you have colorectal cancer based on the results of a routine screening test. Or you might have symptoms that could be caused by colorectal cancer. You will need certain exams and tests to be sure. The process starts with your healthcare provider asking you questions. You'll be asked about your:

  • Health history

  • Symptoms

  • Risk factors 

  • Family history of disease 

Your healthcare provider will also do a physical exam. This will include pressing on your belly (abdomen) You may also have a digital rectal exam (DRE). For a DRE, the healthcare provider puts a gloved, lubricated finger in your rectum to feel for lumps or tumors. They may feel for lymph nodes. Blood and stool tests may be done as well.


If a colonoscopy wasn't the screening test that showed the changes that might be cancer, this test will be needed. First, you'll need to take medicines to clean out all of your colon. They're often started the day before the test. They cause you to pass all of the stool out of your colon until only clear liquid passes through. You will need to use the toilet a lot during this prep.

Medicines will be used to relax you and make you sleepy for the test. A thin, lighted, flexible tube (called an endoscope) is then put into your rectum and through your colon to look at the inside of it. Any growths (polyps) or other areas of change can be removed through the tube to do a biopsy.

What is a biopsy?

A biopsy is the removal of cells or tissue for testing. It can show if the removed tissue has cancer cells in it. For colorectal cancer, a biopsy is the only way to be sure of the diagnosis.

The most common type of biopsy is an endoscopic biopsy. It's often done during a colonoscopy. (Other types of biopsies include a needle biopsy and a surgical biopsy. But these are not often used to diagnose colorectal cancer.)

Once your healthcare provider removes the tissue, they send it to a lab. There a healthcare provider called a pathologist looks at the tissue under a microscope and tests it for cancer cells. It often takes several days for the results of your biopsy to come back. A biopsy is the only sure way to tell if you have cancer. And it's the only way to tell what kind of cancer it is.

Here are the 3 types of biopsies used for colorectal cancer:

Endoscopic biopsy

This is the most common biopsy used to diagnose colorectal cancer. It's done during a colonoscopy or a sigmoidoscopy. These are screening and diagnostic tests that use an endoscope to look at the colon. An endoscope is a thin tube with a small video camera and light on the end. There are types of endoscopes for different parts of the body. For a colonoscopy, the healthcare provider uses a colonoscope. For a sigmoidoscopy, they use a sigmoidoscope. It's shorter and can only reach about 1/3 of the colon.

If the provider finds a polyp or other changes in the colon or rectum during one of these tests, they most likely will remove it. This is done using small tools passed through the endoscope. After cutting the tissue from your colon wall, the provider takes it out through the tube. It's then sent to a lab to be checked for cancer. The lab will then be able to see if any of the growths or changes are cancer.

Needle biopsy

There are 2 types of needle biopsies. One is a fine needle biopsy. The healthcare provider uses a very thin (fine) needle and syringe to remove liquid and a tiny piece of tissue. The other type is a core needle biopsy. This needle is slightly larger. A needle biopsy is sometimes done to take tissue from a tumor found in some other part of your body, like the liver. This test can help show if the cancer has spread.

For a needle biopsy, the provider puts the needle right into the tumor and uses a syringe to pull out a piece of tissue. For tumors the healthcare provider can feel, the biopsy can be done in the provider's office using medicines to numb your skin (a local anesthetic). For tumors that can't be felt, a CT scan can be used to help guide the needle. CT scans are detailed X-rays. Your provider may also use an ultrasound to help guide the needle. These types of biopsies are done in a procedure room. A needle biopsy often takes only a few minutes. You may be given medicine to make you sleepy and not feel pain (sedation) to ease the discomfort. You don’t need to stay in the hospital for these tests.

Surgical biopsy

Most biopsies can be done with one of the above methods. But if the polyp or mass is large or in a hard-to-reach spot, you may need to have surgery. You'll be given general anesthesia so that you fall asleep and don't feel anything during a surgical biopsy. You may also have to stay overnight in the hospital. Depending on the type of surgery needed to reach the tumor, it may be a few days before you can go back to your normal routine.

Getting your test results

Most polyps are benign. This means they're not cancer. The biopsy will show if the polyps or other changes are abnormal cell growths (dysplasia) or cancer (carcinoma).

When your healthcare provider has your biopsy results, they will contact you. Ask when and how you can expect to get this information. Your provider will talk with you about other tests you may need if colorectal cancer is found. This may include imaging tests such as ultrasound, CT, MRI, or PET scans. Make sure you understand the results and what follow-up you need.

Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Online Medical Reviewer: Sabrina Felson MD
Online Medical Reviewer: Todd Gersten MD
Date Last Reviewed: 1/1/2023
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