Diagnosis and Staging of Colorectal Cancer

If your colorectal screening procedure reveals abnormal tissue, you’ll undergo follow-up tests to determine whether you have cancer and whether the cancer has spread. The Washington University Physicians and pathologists at Siteman will ensure that you receive an accurate diagnosis and a comprehensive treatment plan that takes the genetic signature of your cancer into account.

How is colorectal cancer diagnosed?

Colorectal cancer is formally diagnosed through a process called a biopsy. A biopsy usually takes place during a screening test such as a colonoscopy. Tissue samples collected, or biopsied, during the procedure are sent to a pathologist and examined under a microscope. If the pathologist locates cancerous cells in the patient’s tissue, the patient will be diagnosed with colon or rectal cancer.

What happens after I’m diagnosed with colorectal cancer?

Once a patient has been diagnosed with colorectal cancer, it’s important to determine how large the cancer is and how far it may have spread in the body. This process is called staging. You will probably undergo a number of additional tests to stage your cancer.

What tests are used to stage colorectal cancer?

The tests you receive will depend on whether your cancer is located in your colon or rectum. Colon and rectal cancers are staged differently. Because rectal tumors have a greater capacity to impact other organs and parts of the body, they often require additional tests.

Genetic sequencing

Your physicians will genetically sequence your tumor to check for significant genetic mutations that determine how quickly your cancer could spread and how well it might respond to treatment.

CEA blood test

A CEA blood test can help identify the stage of colon cancer. CEA stands for “carcinoembryonic agent.”

CT scan

CT scan images are made by a computer linked to an X-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This test is used to check for the spread of the cancer to places such as the lungs, liver and lymph nodes.


This imaging form uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the colon or rectum. A dye may be injected through a vein so the cancer cells show up more brightly in the pictures.

Patients with rectal cancers sometimes receive pelvic MRIS to assess how far the tumor has spread into the walls of the rectum, whether any lymph nodes have been impacted, and how close the tumor is to other organs and structures in the pelvis.

Rigid proctoscopy and endorectal ultrasound

These procedures are also critical for the staging of rectal cancers. The surgeon inserts a scope into the rectum to determine the exact location of a rectal cancer. An ultrasound probe can also be inserted into the rectum to determine the thickness of the cancer and whether lymph nodes are involved.

What are the stages of rectal cancer?

Like colon cancer, rectal cancer will be assigned a stage from 0 to IV.

Stage 0 (carcinoma in situ)

In stage 0 rectal cancer, the cancer is confined to the inner lining of the rectum. Cancers at this stage usually appear as polyps and can be taken out during a routine colonoscopy. Stage 0 patients sometimes don’t require any additional treatment after the cancerous polyps are removed.

Stage I

Stage I rectal cancer has progressed to the second or third layers of the rectal wall.

Stage II

In cases of stage II rectal cancer, the cancer has advanced through the outermost layer of the rectal wall and may have reached the organs closest to the rectum.  However, the cancer has not yet spread to any lymph nodes.

Stage III

At stage III, the cancer has begun to impact the lymph nodes closest to the rectum.  Small, subsidiary tumors called tumor deposits may also have begun to form in the fat layers of the pelvis.

Stage IV

Stage IV rectal cancer has spread to other organs around the body. This is called metastatic cancer.