Woman holding a blue ribbon for colon cancer

Colon Cancer

Understand the risk factors, signs and symptoms, and tests for colon cancer.

Colorectal cancer (CRC) is a malignant growth of the lower intestine – this is the organ responsible for the removal of water and the formation of solid stool from food waste. The colon is approximately 90 cm. (3 ft.) long and ends at the rectum and anus. In cancer of the colon, cells from the inner lining divide in a rapid and uncontrolled fashion, resulting in a growth that invades local tissues and may spread to other parts of the body.

Unless diagnosed and treated in a timely manner, CRC is fatal. Every year, approximately 23,000 Canadians will be diagnosed with CRC and 9000 will die from this disease. It is the third most common form of cancer behind prostate and breast cancer, as well as the second most common cause of cancer death.

Most cases of CRC develop from pre-existing polyps, which are collections of cells limited to the lining of the bowel, often assuming the shape of a mushroom suspended from the wall. As many as 30% of people have polyps. Luckily, only a small number of these evolve into cancer. The evolution of cancer, including the formation of polyps and the transition to cancer, is a process that can take several years. Polyps and early-stage cancer do not cause symptoms. During this pre-symptomatic period, these early cancers and precancerous growths can be identified and removed, resulting in the prevention and/or cure of colon cancer.

Illustration of a polyp in the colon
illustration of polyps and cancer

Risk Factors for Colon Cancer

  • Age is an important risk factor – over 90% of CRC cases occur in individuals over the age of 50.
  • While both sexes are affected, CRC affects males significantly more frequently than females.
  • People of African descent may be more susceptible to CRC.
  • A personal history of CRC increases the risk for a second cancer of the colon.
  • A family history of CRC, particularly affecting younger individuals, or multiple cases within a family.
  • Inherited cancer family syndromes, including familial adenomatous polyposis, Lynch syndrome and others.
  • People with inflammatory bowel disease (ulcerative colitis and Crohn’s disease) develop CRC much more frequently than the general population.
  • Certain lifestyle factors appear to modestly increase the risk for CRC. These include obesitylack of physical activity and tobacco usage. There is some evidence that a diet high in animal fat and low in fruits and vegetables may increase risk.
  • Low dose aspirin MAY lower the risk of polyps and CRC.
  • Failure to participate in a screening programme as described below. Persons who do not undergo screening are much more likely to develop CRC than those who do, because removal of polyps identified during screening serves as an effective preventative measure.

Healthy Gut Summit 2016 presentation by Dr. David Armstrong on protecting yourself from Colon Cancer.

Polyps and early-stage CRC do not produce symptoms, with the exception of visible blood in stool when situated close to the bottom of the colon. As cancers grow, they begin to affect the activity of the colon resulting in:

  • Blood in stool
  • Anemia (low red blood cell count) from progressive blood loss, manifesting as fatigue
  • Persistent change in bowel movements, with looser and more frequent stools (diarrhea) or less frequent stools (constipation)
  • A sensation of fullness in the rectum or the persistent feeling of having to move (or empty) one’s bowels
  • Cramps, abdominal discomfort or bloating with cancers that partially block the bowel
  • Weight loss, decreased appetite, nausea and vomiting with more advanced cancers.

In most instances, the symptoms described above do not prove to be due to CRC. However, the onset of any of these should prompt a visit to your physician to carry out the appropriate examinations to identify or exclude colon cancer. If in doubt, go to your physician.

How is Colon Cancer Diagnosed?

If you have symptoms that are potentially indicative of CRC, see your family physician. They will carry out a physical examination, particularly looking for palpable masses in the abdomen suggesting cancer. They may also carry out a digital rectal examination to detect cancer of the rectum, particularly if there has been blood in stool.

Your family doctor may elect to arrange imaging studies such as abdominal ultrasound or computerized axial tomography (CAT scan), but the sensitivity of these tests for CRC (particularly in its early stages) is low. More importantly, your family doctor will refer you to a specialist who can carry out visualization of the colon, usually by colonoscopy.

Colonoscopy involves the passage of a long, flexible instrument (colonoscope) via the anus through the length of the colon. The tip of the colonoscope has a light which illuminates the interior, as well as a video chip which transmits an image to a monitor for the doctor to view. There is also a channel through the colonoscope that enables the passing of instruments, most notably a forceps which can take tissue samples from suspicious masses and a snare (or wire loop) which can grasp polyps and remove them from the lining of the bowel. Colonoscopy will identify roughly 98% of cancers. A normal colonoscopy very strongly excludes the presence of cancer and provides strong reassurance that CRC will not be a possibility for several years down the road, since the evolution of CRC from normal tissue is a very slow process.

The investigations below are available for people unable or unwilling to undergo colonoscopy. These examinations are somewhat less accurate than a colonoscopy in detecting growths and have no capability of removing polyps or confirming cancer by tissue sampling. Therefore, if a suspicious abnormality is identified, colonoscopy may still be recommended prior to more invasive surgical exploration:

  • Flexible sigmoidoscopy (FS), using a shorter viewing instrument which can visualize up to 60 cm. of the lower colon, performed with a simple preparation and without sedation. This option is not nearly as comprehensive, but might be utilized where colonoscopy is not readily available.
  • Barium enema in which the colon is filled with a radio-opaque material and X-rays are taken. A cleansing routine similar to colonoscopy is necessary.
  • CT colonography, also called virtual colonoscopy, in which computerized tomographic images are taken after the colon is filled with air from below. The procedure requires a cleansing preparation similar to colonoscopy but does not need sedation.  
  • Magnetic resonance (MR), a relatively new way of imaging the colon using an MRI scanner.

Screening for Colon Cancer

If you have no symptoms and are not at increased risk, you should still consider getting a screening examinationBecause screening is so proficient at identifying CRC and precancerous polyps, it is among the most effective preventive medical interventions.  While there is controversy about which screening strategy is best, there is consensus that persons who engage in CRC screening have a longer life expectancy than those who do not, as a result of early diagnosis and treatment of CRC and removal of polyps before they turn malignant.

Current guidelines recommend commencing screening at age 50 and continuing to age 75. Whether to continue screening thereafter depends on one’s state of health and life expectancy.

There are two pre-eminent approaches to screening:

  • FIT (fecal immunochemical test) is directed towards detecting blood in stool and is based on the observation that most cancers and some advanced polyps shed small amounts of blood – not enough to be seen with the naked eye. A small sample of stool is smeared on a slide, which is submitted to a laboratory to analyze for the presence of blood. FIT testing is not appropriate for persons who have visible blood in stool and should not be carried out in the presence of blood thinners or non-steroidal anti-inflammatory drugs such as aspirin. The approximately 5% of persons with a positive FIT test are referred for colonoscopy to determine whether the blood loss is emanating from a tumour of the colon. If the colonoscopy is normal, no further screening is necessary for 10 years. Those with a negative FIT test should have it repeated at two-year intervals. The advantages of FIT are low cost, the relatively high participation rate, and its absolute safety and lack of invasiveness. The disadvantages are its failure to detect all cancers, its limited ability to detect and remove pre-cancerous polyps, and its dependence on repeated testing to achieve maximal benefit. Many provincial bodies advocate FIT as the preferred approach to screening.
  • Colonoscopy is the direct examination of the colon using a flexible videoendoscope. Colonoscopy detects the vast majority of cancers, most of which are curable by resection, either through the colonoscope for cancer confined to a polyp or by open surgical resection for more invasive tumours. If colonoscopy is normal, no further screening is required for 10 years. However, if polyps or cancer are identified, careful follow-up by colonoscopy is indicated, as a history of polyps enhances the risk for future CRC. The timing of follow-up is dependent on the characteristics of the tumour. The doctor performing the colonoscopy will advise you on the appropriate interval. The advantages of colonoscopy include its high detection rate for cancer and its potential to prevent cancer by removal of polyps. In addition, the benefit is long-lasting – the procedure need be carried out relatively infrequently. The disadvantages are the cost, the complex preparation, the need to take time from work, and the potential for complications.

These options should first be discussed with a family physician. Personal comfort level, as well as age, state of health and family history should be taken into consideration.

Guideline for Colorectal Screening

Canadians with family history of colorectal cancer need to be screened earlier, more often.  The Canadian Association of Gastroenterology (CAG) has released a guideline for colorectal screening. 

There is evidence that people with first degree relatives (parents, brothers, sisters or children) with colorectal cancer are at an increased risk.

Checking for evidence of a disease in a group of people who do not show any symptoms is done through a screening program.  In Canada, each province has a program to screen a portion of the population for Colorectal Cancer.  Screening helps to identify cancer, often before any symptoms develop in an individual.  An individual’s prognosis, or chances of successful treatment, are much better when colorectal cancer is found and treated early.  In general, individuals who are between 50 and 74 years of age, or who have a higher risk for colorectal cancer, participate in a screening program. 

Read more about your provincial colorectal cancer screening program.

Download CAG’s Guideline for Colorectal Screening.

Staging and Treatment of Colon Cancer

CRC is classified according to how far it has spread into and beyond the wall of the bowel. In the earliest stage, cancer has not penetrated through the wall and is curable by resection with no further therapy. If CRC has grown beyond the confines of the bowel into adjacent tissues, or if cancer has spread to local lymph nodes, it is likely that, following surgery to remove the primary tumour, further treatment in the form of radiation or chemotherapy (anti-cancer drugs) will be recommended. In the most advanced stage, cancer has spread via the blood stream to remote sites. In this circumstance, chemotherapy may be recommended to delay the progression of cancer, but definitive cure is unlikely.

For cancers arising in the rectum, radiation therapy is often recommended prior to surgery. Evidence suggests that this approach can shrink the tumour preoperatively and increase the likelihood of successful removal.

What to Know about Colonoscopy

Colonoscopy involves the passage of a long, flexible instrument, via the anus, approximately 90 cm (3 ft) through the length of the colon. The instrument has a source of light that illuminates the inside of the bowel, and a mechanism to distend the bowel with air for better visualization. There is a channel for the passage of accessories that can remove polyps, take tissue samples (biopsies) from suspicious areas and cauterize bleeding points. The examination is carried out in a specialized room designed to maximize safety and comfort. Most procedures are carried out sedated – this means you will receive an injection immediately beforehand that will make you sleepy and diminish any sensation of pain or recollection of the examination. Colonoscopy time averages 20-30 minutes.

An effective colonoscopy depends on good visibility. For this reason, the examination requires meticulous preparation. For the 24 to 48 hours prior to your examination, you will be instructed to engage in measures that include a liquid diet and a combination of laxatives. It is crucial that you adhere carefully to the instructions to optimize the examination.

Screening colonoscopy aims to identify cancer and to remove precancerous polyps. Polyps with a stem or stalk (pedunculated) can be removed during colonoscopy with electrocautery applied to a wire loop.

Suspicious lesions without a stalk can be biopsied. If biopsies reveal cancer, removal requires formal surgery.

While colonoscopy is generally considered a safe procedure, there are potential complications. Those directly related to the colonoscope itself include bleeding, usually from the site from which polyps have been taken. Such bleeding often stops on its own or with the application of cauterizing material through the colonoscope. Very rarely, bleeding is delayed and may start up after discharge from the procedure area. In that instance, a return to the endoscopy unit could be necessary. Another risk is perforation, or a hole in the bowel resulting from distension or the application of cautery used in the removal of polyps. Perforation is reported to occur approximately one in every 2000 colonoscopies and is usually manifested by severe pain immediately following the procedure. Rarely, the symptoms of perforation, as for bleeding, may be delayed. Should you experience substantial bleeding or progressive and severe pain after discharge from colonoscopy, you should contact the unit or go to an emergency department immediately.

If polyps are removed during colonoscopy, they are retrieved and sent for microscopic (pathology) examination. The results of this examination determine when one’s next colonoscopy should take place. Some polyps, termed hyperplastic, have no firm relationship to cancer and do not require early re-examination. Other polyps are termed adenomatous and will trigger a recommendation for a follow-up colonoscopy between one and five years later. The overall effectiveness of a screening regimen with colonoscopy is highly dependent on timely follow-up. If the interval advised is too short, the benefit of screening will be compromised by the expense and the hazards of too many exams. If the interval is too long, the risk of developing an incurable cancer during follow-up becomes significant. Therefore, should you have polyps removed during your colonoscopy, be sure that the pathology report is a part of your records, and available when consideration of a repeat colonoscopy arises down the road.

Proper Bowel Prep Can Save Your Life

Too many people skip potentially life-saving procedures because of misunderstandings and misconceptions about the bowel prep. However, most people who have had colonoscopies, will tell you it isn’t nearly as bad as you think and that the benefits far outweigh the risks. Robbie, Anne and Laurie, who range in age from 11 to 80 years, openly share their experiences with you in this video.

Some statistics on colon cancer:

  • Download the 2021 Canadian Cancer Statistics
  • Colorectal cancer is expected to be the third most commonly diagnosed cancer in Canada in 2021 (excluding non-melanoma skin cancers). It is the second leading cause of death from cancer in men and the third leading cause of death from cancer in women in Canada.

It is estimated that in 2021:

  • 24,800 Canadians will be diagnosed with colorectal cancer. This represents 11% of all new cancer cases in 2021.
  • 9,600 Canadians will die from colorectal cancer. This represents 12% of all cancer deaths in 2021.
  • 13,700 men will be diagnosed with colorectal cancer and 5,300 will die from it.
  • 11,100 women will be diagnosed with colorectal cancer and 4,300 will die from it.
  • On average, 68 Canadians will be diagnosed with colorectal cancer every day.
  • On average, 26 Canadians will die from colorectal cancer every day.
  • It is estimated that about 1 in 14 Canadian men will develop colorectal cancer during their lifetime and 1 in 34 will die from it.
  • It is estimated that about 1 in 18 Canadian women will develop colorectal cancer during their lifetime and 1 in 40 will die from it.

For more information about cancer statistics, go to Canadian Cancer Statistics.


Colorectal cancer statistics https://www.cancer.ca/~/media/cancer.ca/CW/cancer%20information/cancer%20101/Canadian%20cancer%20statistics/Canadian-Cancer-Statistics-2017-EN.pdf?la=en

Am I going to die if I am diagnosed with colon cancer?

Survival is closely linked with the stage of the disease at the time of surgery. When cancers are still localized to the bowel, the 5-year survival rate is very good — about 85-95%. Unfortunately, by the time colon cancer causes advanced symptoms, most cancers have spread beyond the bowel and the survival rate is less than 40%. Screening, therefore, is designed to detect and remove polyps early while they are can be completely removed.

How is colon cancer prevented?

It is now well established that effective colon cancer screening using stool tests, sigmoidoscopy and colonoscopy can prevent colon cancer. These screening methods lead to detection and removal of polyps and small cancers that can be easily removed. The use of screening is critical to the prevention of colon cancer.

Is it true that taking aspirin can reduce the risk of colon cancer?

No, a recommendation has not been made by the Canadian Association of Gastroenterology about taking ASA for cancer prevention for the following reasons:

  1. The evidence of ASA reducing the risk of colon cancer is largely circumstantial. While interesting, there have been no actual trials designed to look at colon cancer reduction with ASA.
  2. There are hazards associated with taking ASA, including bleeding in the intestinal tract, which are typically at par with the reduction of risk of cancer.

People may think that if they are taking ASA as a preventative measure, they may not go for standard screening which should not be missed if you are over 50, have a family history of colon cancer or polyps, or suffer from inflammatory bowel disease. Colon cancer is over 90% preventable if detected early.

What is the difference between a colonoscopy and sigmoidoscopy?

The difference between colonoscopy and sigmoidoscopy is related to which parts of the colon each can examine. Sigmoidoscopy allows doctors to view only the lower part of the colon, while colonoscopy allows doctors to view both the upper and lower sections. Recent research suggests that colonoscopy is superior to flexible sigmoidoscopy as a colon cancer screening method.

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