Diagnosis and Staging of Colorectal Cancer

If your screening reveals any abnormalities, 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 are experts in diagnosing colorectal cancer and will ensure that you receive a comprehensive treatment plan that takes the genetic signature of your cancer into account.

Diagnosing colorectal cancer

When it comes to diagnosing colorectal cancer definitively, doctors usually need to perform a biopsy. A biopsy usually takes place during a screening test such as a colonoscopy. Any tissue samples that the doctor collects during the procedure are sent to a pathologist, who will examine them under a microscope. If the pathologist finds cancerous cells in the patient’s tissue, the patient will receive a colon or rectal cancer diagnosis.

What happens after a colorectal cancer diagnosis?

Once you’ve received a diagnosis of colorectal cancer, it’s important to determine how large the cancer is and how far it may have spread in your body. This process is called staging. You will probably undergo a number of additional tests to stage your cancer. The tests you receive will depend on whether your cancer is located in your colon or rectum.

The staging processes for colon and rectal cancers are different. Because rectal tumors have a greater capacity to impact other organs and parts of the body, they often require additional tests. These tests may include genetic sequencing, CEA blood test, CT scan, MRI, and rigid proctoscopy and endorectal ultrasound.

Types of genetic tests

What is 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.

What is a CEA blood test?

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

What is a CT scan?

A CT scan uses computerized X-ray technology to produce images of the body’s internal structures. Your doctor may inject a dye into a vein or have you drink a solution containing a contrast agent to help your organs or tissues show up more clearly. This test checks for the spread of the cancer to places such as the lungs, liver and lymph nodes.

What is an MRI?

Magnetic resonance imaging (MRI) uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the colon or rectum. Your doctor may inject a dye into 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 the cancer has spread to any lymph nodes and how close the tumor is to other structures in the pelvis.

What is a 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. The surgeon can also insert an ultrasound probe into the rectum to determine the thickness of the cancer and whether it has spread to any lymph nodes.

Stages of rectal cancer

Like colon cancer, rectal cancer is assigned a stage from 0 to IV:

Stage 0 (carcinoma in situ): the cancer hasn’t grown beyond 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: the cancer has progressed to the second or third layers of the rectal wall. It hasn’t yet spread to nearby areas.

Stage II: the cancer has advanced through the outermost layer of the rectal wall and may have reached the organs closest to the rectum.  However, it hasn’t yet spread to any lymph nodes.

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: the cancer has spread to other organs around the body. This is called metastatic cancer.