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Diagnosis of colorectal cancer
Diagnosis is the process of finding out the cause of a health problem. Diagnosing colorectal cancer usually begins with a visit to your family doctor. Your doctor will ask you about any symptoms you have and may do a physical exam. Based on this information, your doctor may refer you to a specialist or order tests to check for colorectal cancer or other health problems.
The process of diagnosis may seem long and frustrating. It’s normal to worry, but try to remember that other health conditions can cause similar symptoms as colorectal cancer. It’s important for the healthcare team to rule out other reasons for a health problem before making a diagnosis of colorectal cancer.
The following tests are usually used to rule out or diagnose colorectal cancer. Many of the same tests used to diagnose cancer are used to find out the stage (how far the cancer has spread). Your doctor may also order other tests to check your general health and to help plan your treatment.
Health history and physical exam
Your health history is a record of your symptoms, risk factors and all the medical events and problems you have had in the past. Your doctor will ask questions about your history of:
- symptoms that suggest colorectal cancer
- polyps in the colon or rectum
- familial adenomatous polyposis (FAP)
- Lynch syndrome (also called hereditary non-polyposis colorectal cancer or HNPCC)
- inflammatory bowel disease (IBD)
Your doctor may also ask about a family history of:
- colorectal cancer
- risk factors for colorectal cancer
- other cancers
A physical exam allows your doctor to look for any signs of colorectal cancer. During a physical exam, your doctor may:
- feel the abdomen for lumps and enlarged organs
- do a digital rectal exam (DRE)
Find out more about a physical exam.
Digital rectal exam (DRE)
DRE is an exam in which the doctor inserts a gloved finger into the rectum to check for lumps or swelling, or to measure how far a rectal tumour is from the anus. DRE is used with a transrectal ultrasound or pelvic MRI to find out the stage of the rectal cancer, including how deep the tumour has grown into the wall of the rectum.
Find out more about a digital rectal exam (DRE).
Complete blood count (CBC)
A CBC measures the number and quality of white blood cells, red blood cells and platelets. A CBC is done to check for anemia from long-term (chronic) bleeding.
Find out more about a complete blood count (CBC).
Blood chemistry tests
Blood chemistry tests measure certain chemicals in the blood. They show how well certain organs are functioning and can help find abnormalities.
Liver function tests measure how well the liver is working. Higher levels of certain substances may mean that colorectal cancer has spread to the liver.
Find out more about blood chemistry tests.
Tumour marker tests
Tumour markers are substances found in blood, tissues or fluids removed from the body. An abnormal amount of a tumour marker may mean that a person has colorectal cancer. Tumour marker tests are also used to check your response to cancer treatment.
The following tumour markers may be measured for colorectal cancer:
Stool tests check for hidden (occult) blood in the stool. A guaiac-based fecal occult blood test (gFOBT) or a fecal immunochemical test (FIT) may be done during diagnosis if it was not used during screening.
Find out more about stool tests.
Double-contrast barium enema
A double-contrast barium enema is an imaging test that uses a special substance (barium sulphate) and x-rays to make images of the entire large intestine (cecum, colon, rectum and anus). Air is pumped into the intestine to improve the view. It can show polyps or growths in the colon.
A double-contrast barium enema may be done if a stool test shows occult blood or if you have bleeding from the rectum, blood in the stool or abdominal pain.
Find out more about a barium enema.
Sigmoidoscopy is a procedure that uses a thin, tube-like instrument with a light and lens on the end (called an endoscope). It is used to look at the sigmoid colon (the last part of the colon) and the rectum. A biopsy sample may be collected during a sigmoidoscopy. A sigmoidoscopy may be done if you have symptoms of colorectal cancer.
Find out more about a sigmoidoscopy.
A colonoscopy is the most common test used to diagnose colorectal cancer. During a colonoscopy, the doctor looks inside the colon and rectum using a flexible tube with a light and lens on the end (called an endoscope).
A colonoscopy is done if you have symptoms of colorectal cancer or to check polyps or other abnormal areas that were found during a barium enema or sigmoidoscopy. A biopsy sample may be collected during a colonoscopy.
Find out more about a colonoscopy.
During a biopsy, the doctor removes tissues or cells from the body so they can be tested in a lab. A report from the pathologist will show whether or not cancer cells are found in the sample.
A biopsy is usually done during a colonoscopy or sigmoidoscopy (called an endoscopic biopsy) to remove polyps or small amounts of tissue from the colon or rectum. A core biopsy may be used to collect samples from organs where the cancer may have spread, such as the liver.
Find out more about biopsies.
Cell and tissue studies
Cells and tissue studies look closely at the cells of a tumour to find out the type of colon or rectal cancer. They can also show certain changes or characteristics in the body. Cells may be collected from blood or urine. They can also come from tissue samples collected with biopsy or other procedures.
KRAS is a gene that can be changed (mutated) in some colorectal cancer cells. The KRAS test is usually done on colorectal tumours that have spread (metastasized) because it may show if targeted therapy is a treatment option. Colorectal tumours that have the KRAS gene mutation are unlikely to respond to the targeted therapy drugs.
Microsatellite instability (MSI) is a change to the DNA in a cell. Normally, mismatch repair (MMR) genes correct any mistakes to DNA that happen when it’s copied during cell division. When the MMR genes don’t work properly, MSI can happen. People with Lynch syndrome have a mutation in one of their MMR genes. A colorectal tumour may be tested for MSI to find out if the tumour could have been caused by Lynch syndrome.
Find out more about cell and tissue studies.
A computed tomography (CT) scan uses special x-ray equipment to make 3D and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures.
A CT scan is used to check if colorectal cancer has spread to lymph nodes or organs in the chest, abdomen and pelvis. A CT scan of the pelvis may be used to measure how far a rectal tumour is from the anus. A biopsy sample may be collected during a CT scan to see if cancer has spread to organs such as the liver.
A virtual colonoscopy uses a CT scan to make images of the colon and rectum without using an endoscope. If virtual colonoscopy equipment is available, you may be offered this test if you can’t have a regular colonoscopy.
Find out more about CT scans.
An ultrasound uses high-frequency sound waves to make images of parts of the body. It may be used to check if colorectal cancer has spread to the liver.
A transrectal ultrasound (TRUS), also called endorectal ultrasound, places an ultrasound probe inside the rectum. It is used to find out the stage of rectal cancer, including how deep the tumour has grown into the wall of the rectum and to measure how far a rectal tumour is from the anus.
Magnetic resonance imaging (MRI) uses powerful magnetic forces and radiofrequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3D pictures.
An MRI of the pelvis may be used to find out the stage of rectal cancer and where it has spread within the pelvis. It may also be used to measure how far a rectal tumour is from the anus.
Find out more about MRIs.
An x-ray uses small doses of radiation to make an image of parts of the body on film. A chest x-ray is used to check if colorectal cancer has spread to the lungs.
Find out more about x-rays.
A positron emission tomography (PET) scan uses radioactive materials called radiopharmaceuticals to look for changes in the metabolic activity of body tissues. A computer analyzes the radioactive patterns and makes 3D colour images of the area being scanned.
A PET-CT scan combines images from a PET scan and a CT scan, which are done at the same time using the same machine. It may be used to help with staging colorectal cancer or to plan surgery for metastatic tumours.
Questions to ask your healthcare team
familial adenomatous polyposis (FAP)
An inherited condition that causes hundreds to thousands of polyps to develop, mainly on the lining of the colon and rectum.
People with FAP have a higher risk of colorectal cancer and small intestine cancer. It also increases the risk of stomach, adrenal gland and thyroid cancers.
An inherited condition that causes a large number of polyps to develop in the lining of the colon and rectum but not as many polyps as are found in familial adenomatous polyps (FAP).
There are 2 types of Lynch syndrome. Type A increases the risk for colorectal cancer, and type B increases the risk of several cancers, including colorectal cancer and other digestive system cancers, and ovarian and uterine cancers in women.
Also called hereditary non-polyposis colorectal cancer (HNPCC).
deoxyribonucleic acid (DNA)
The molecules inside the cell that program genetic information. DNA determines the structure, function and behaviour of a cell.