How is colorectal Cancer diagnosed?
If a colorectal cancer screening test such as a fecal immunochemical test (FIT) has come back with abnormal results, or if you are experiencing symptoms, additional testing is required to check for the presence of colorectal cancer. Once all the outcomes have been put together, your doctor will review these results with you.
One or more of the following tests and procedures will be performed to rule out or diagnose colorectal cancer:
Colonoscopy
An endoscopist uses a flexible tube (colonoscope) that has a small light and camera at one end to look at the entire length of the inside of your large intestine (colon and rectum). If abnormal tissue is found, samples will be taken and sent for biopsy.
Biopsy
A biopsy is done by a pathologist on a tissue sample from your colon or rectum that is usually removed during a colonoscopy. A biopsy analyzes the tissue in a laboratory to determine whether cancer cells are present.
Flexible Sigmoidoscopy
Similar to a colonoscopy except that instead of visualizing the entire colon, the sigmoidoscopy only examines the lower portion of the colon (sigmoid colon) and the rectum.
Digital Rectum Exam
This is an examination of your back passage (rectum), which involves your doctor feeling inside your rectum using their finger.
Blood Tests
While blood tests are not used to make a colorectal cancer diagnosis, they can provide insight into someone’s overall health and point to issues that may be connected to the presence of cancer. For example, a blood test might show that someone has a low number of red blood cells, which could be tied to a colorectal tumour that is causing bleeding.
Radiology / Nuclear Exams
Many of the same tests used to diagnose cancer are used to determine the Stage. Other tests include:
A CT scan is a test that uses x-rays and a computer to create detailed pictures of the cancer. It takes pictures from different angles, and a computer puts them together to make a 3-dimensional (3D) image.
A PET scan is an imaging test that uses a radioactive drug (tracer) to show the activity of the tissues and organs of the body. The tracer may be injected, swallowed or inhaled, depending on which organ or tissue is being studied. The tracer collects in areas of the body that have higher levels of chemical activity, which often correspond to areas of disease. On a PET scan, diseased areas such as cancer show up as bright spots.
Sometimes CT and PET are combined:
A PET CT scan combines a CT scan and a PET scan into one to give more detailed information about your cancer. These scans may also be combined with an MRI scan.
MRI (magnetic resonance imaging) uses magnetism and radio waves to create cross sectional pictures of the body. It produces pictures from angles all around the body and highlights soft tissues very clearly.
Most commonly done for rectal cancer, this scan uses ultrasonic sound waves to look at the inside of your rectum. This could give information to your doctor such as how far it has grown through the rectal wall, and whether it has spread further.
Similarly, this scan uses ultrasonic sound waves to look at the abdomen and check if the cancer has spread there.
Radiology / Nuclear Exams
Many of the same tests used to diagnose cancer are used to determine the Stage. Other tests include:
