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Colon cancer screening is the key to early detection

Colon cancer is the third most commonly diagnosed cancer in Canadian women, and the third leading cause of cancer deaths, after lung cancer and breast cancer.

The good news is that the survival rate for colon cancer is very high – 90 per cent – when it is detected early. That’s why screening is so important: the goal is to find cancer while it is still in these early stages, when treatment is very successful.

Screening may also identify polyps, which are growths on the inside wall of the colon that can develop into cancer. This development is a slow process, taking 10 years or more for a polyp to form from normal tissue, and then progress to cancer. Finding and removing polyps before they progress can prevent the cancer from ever developing.

Screening programs are for people at average risk, and who don’t have any symptoms of colon cancer. If you do have symptoms of colon cancer – such as rectal bleeding, blood in the stool, changes in bowel habits, or abdominal pain – see your doctor.

“We consider an average risk person to be someone who doesn’t have any family members who have colon cancer or colon polyps, and someone who they themselves have never had any colon cancer or colon polyps,” says Women’s College Hospital gastroenterologist Dr. Talia Zenlea. “For people at average risk, we typically recommend screening starting at age 50.”

Screening options

The two most common methods of screening in Ontario are fecal occult blood testing (FOBT) and colonoscopy.

Fecal occult blood testing looks for tiny amounts of blood in the stool. Samples are collected using a take-home kit.

“You are given a card to do at home and then mail back,” explains Dr. Zenlea, whose BellyBlog.ca website offers GI and health information from medical experts. “It's meant to identify any blood that may not be visible to the naked eye. If it’s positive, that can sometimes be indicative of something more concerning, and it would warrant a colonoscopy for further investigation.”

FOBT is the test currently used in Ontario, but many other parts of Canada use a fecal immunochemical test (FIT) instead. FIT is expected to replace FOBT in Ontario in summer 2019. Like FOBT, FIT is a stool test that is done at home. It also tests for tiny amounts of blood in the stool, but it uses a different chemical process to detect blood, and is much more accurate at detecting large polyps, with fewer false positives. 

For some people, it might be appropriate to screen using colonoscopy instead of fecal occult blood testing.

“The advantage of colonoscopy is that it actually prevents colon cancer,” Dr. Zenlea says. “We’re not just looking for a flag of something more concerning. We’re preventing cancer by taking out polyps which have the potential to form into cancer if left in place over time. During the procedure, we would actually take those polyps out then and there and prevent colon cancer.”

The other advantage of a colonoscopy is that if the results are normal, you don’t have to be screened again for 10 years. Fecal occult blood testing is repeated every year or every two years.

The advantages of fecal occult blood testing over colonoscopy is that it’s not an invasive test.

“Fecal occult blood testing is something that you can do at home. You don’t need to be sedated, there’s no preparation involved, and you don’t subject yourself to any procedural risk,” Dr. Zenlea says.

You may also have the option of having a flexible sigmoidoscopy. Like a colonoscopy, this procedure uses a small camera to look at the inside of the colon. The difference is that while a colonoscopy looks at the whole colon, a sigmoidoscopy only looks at the lower part of the colon. While it is not as thorough as a colonoscopy, a flexible sigmoidoscopy also does not require sedation or extensive preparation.

Increased risk

People who have had colon cancer or polyps in the past, or who have close relatives with a history of colon cancer or polyps, are considered at increased risk for colon cancer. Close relatives are first-degree relatives, which include parents, siblings and children.

Screening guidelines are different for this group. It’s recommended that people at increased risk begin screening with colonoscopy at a younger age: either age 40, or at 10 years younger than the age at which a relative had colon cancer – whichever comes first.

“So the latest it would ever be would be age 40,” Dr. Zenlea explains. “But if your relative had colon cancer at the age of 45 then we would want to see you 10 years before that, so at age 35. Depending on the findings of your own colonoscopy, you might have to come back more frequently, but that’s individualized based on the findings and your family history.”


Quick Guide to Colon Cancer Screening

For people at average risk

Begin screening at age 50 with either:

•             fecal occult blood test (FOBT)

•             colonoscopy

Average risk describes someone who:

•             has never had colon cancer or colon polyps

•             has no close family members who have had colon cancer or colon polyps

For people at increased risk

Begin screening with colonoscopy at the younger age of these options:

•             age 40, or

•             10 years younger than a family member was diagnosed with colon cancer

Increased risk describes someone who:

•             has a history of colon cancer or colon polyps

•             has one or more close family members who have had colon cancer or colon polyps


This information is provided by Women’s College Hospital and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition. This document was last reviewed on: Apr. 29, 2019.

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