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Colon cancer (colorectal cancer) Causes, Symptoms and Treatment

As its name suggests, colorectal cancer is formed in the colon or rectum , the last part of the large intestine .

The colorectal cancer reaches the 3 among the most common cancers in Canada, both in men than in women. One in 14 men and 1 in 15 women are at risk of colorectal cancer in their lifetime.

Colorectal cancer is much more common in industrialized countries. Lifestyle habits, mainly diet , play a key role in its appearance. This explains, for example, that the Japanese, little affected by colorectal cancer in Japan, become as much as their fellow Americans a few years after emigrating to the United States and adopted their diet.

Some people may contract it because of a hereditary predisposition . But in 75% of cases, heredity is not in question.

Evolution of Colon cancer

The colorectal cancer takes years to form, as the majority of cancers. It usually does it from polyps in the wall lining the inside of the colon . Polyps are small, fleshy growths. There are several kinds of it. Most often, they are benign. However, we know that some of them can become cancerous. It takes an average of 10 years for a polyp to form a cancerous tumor. Polyps (cancerous or not) sometimes cause digestive discomfort . For more information, see our leaflet Intestinal Polyps.

As soon as the doctor detects polyps in a patient, he conducts tests to see if they pose a risk to his health.

At an advanced stage of development, colorectal cancer can spread to the lymph nodes, then to the liver and then to other parts of the body, forming metastases .

In Canada, colorectal cancer is the the  leading cause of death by cancer. The death rate 5 years after diagnosis is about 40%, in both sexes.

Currently, more than half of cases are diagnosed in people aged 70 and older. Health professionals would like more people to be screened regularly by the age of 50, and earlier for people at risk. The earlier the cancer is detected, and it is possible to do so before the onset of symptoms, the better the chances of recovery .

When to consult

If there is blood in the stool or persistent diarrhea or constipation , it is important to consult a doctor. For people at risk, it is advisable to be tested. Discuss with your doctor.

Symptoms of Colon cancer

The colorectal cancer usually goes unnoticed in its early stages of growth. The following symptoms may be a sign of colorectal cancer.

  • The changes in fecal habits that last for a few weeks (constipation or diarrhea, for example).
  • The blood in the stool.
  • Abdominal discomfort, such as intestinal gas, cramps or stomach pain.
  • The sensation that the intestines can never be completely emptied or constantly wanting to defecate.
  • A great fatigue .
  • weight loss unexplained.
Note . Be aware that the presence of blood in the stool may have another explanation, such as hemorrhoids or an anal fissure. In addition, some foods may stain stools. This is the case of beets, for example.

People at risk Colon cancer

  • People over 50 (90% of cases).
  • Personal or family history . The risk increases when someone has already had colorectal cancer or polyps , or a close family member (mother, father, brother or sister) has suffered. This predisposition is not always of hereditary origin. It can be the result of exposure to the same carcinogenic substance in the environment, or dietary habits or lifestyle.Some genetic diseases of the colonincrease the risk of colorectal cancer. The two most common forms are hereditary non-polyposis colorectal cancer (or Lynch syndrome), responsible for about 5% of colorectal cancer cases, and adenomatous familial polyposis, which is involved in about 1% of cases. The latter is manifested by the appearance of a very large number of polyps, from adolescence.
  • Inflammatory bowel disease . Being diagnosed with Crohn’s disease or ulcerative colitis increases the risk.
  • Diabetes . In epidemiological studies, it has emerged that colorectal cancer is more common in individuals with type 2 diabetes than in those without.
  • Lack of exposure to the sun . It seems that the risk of getting colon cancer is higher in parts of the world where people are less exposed to the sun. It is believed that the protective effect is due to vitamin D, produced by the sun’s rays on the skin.

Risk factors

Some lifestyle habits contribute to colorectal cancer.

  • Smoking and high alcohol consumption.
  • Overweight or obesity.
  • Sedentary lifestyle.
  • Diet rich in red meat, charcuterie and barbecue grills, and low in fruits and vegetables.
Psychological factors

The role of the psychological state in the appearance of cancer is controversial. Certain personality traits have been associated in studies with an increased risk of cancer. However, other studies have come to contradict this hypothesis. For more information, see our Cancer fact sheet.

Prevention of colon cancer

Screening measures
To undergo a screening test after the age of 50 years. If 60% of people aged 50 to 74 years pass such a test every 2 years, it is estimated that the number of deaths from colorectal cancer could be reduced from 15% to 18%.

It is with this in mind that the Quebec Ministry of Health and Social Services is currently working on the implementation of a screening program that will target all people aged 50 to 74. This program will meet the criteria we describe below.

  • People concerned: men and women over 50 years old.
  • Fecal occult blood test (FOBT). Any of the following techniques can be used to detect traces of blood in the stool, invisible to the naked eye.
    – Guaiac test  : done at home, it requires the taking of stool samples, spread on a small cardboard coated with guaiac, a plant substance. The cardboard is then given to the doctor or sent to the laboratory for analysis by a technician.
    – Immunochemical test(TIRSOS): The saddle samples are analyzed differently. This new test is more accurate because it only detects blood from the colon or rectum (and not from any part of the digestive tract, as does guaiac). In addition, it has the advantage of not requiring restrictions in the intake of food and medication in the days leading up to the test.
  • Frequency: every year or 2 years.
  • When this test is positive, other medical examinations are offered. The sigmoidoscopyflexible probe allows the physician to observe the wall of the rectum and sigmoid colon (see diagram). The colonoscopy allows an examination of the rectum and all sections of the colon. It is practiced under analgesic medication. These two exams make it possible not only to visualize the wall of the rectum and the colon, but also to remove the polyps that are there and thus prevent the appearance of possible cancers. These exams are not only preventive, they are actually curative.

For people at risk . In the case of a family history of colorectal cancer or inflammatory bowel disease, for example, it may be advisable to have a sigmoidoscopy or colonoscopy at the age of 40 years. Discuss with your doctor.


Basic preventive measures
  • Do not smoke . To find out about various ways that make it easier to stop, check our Smoking Sheet.
  • Stay physically active Physical activity (moderate and intense) would reduce risk by up to 50%.
  • Achieve or maintain a healthy weight . To know your body mass index, do our BMI test.
  • Limit alcohol consumption . The Canadian Cancer Society recommends that women limit their alcohol consumption to less than 1 drink per day and men less than 2 drinks per day.
  • Eating enough fruits and vegetables and whole grain cereals seems to help prevent colorectal cancer. These foods contain vitamins, minerals, fiber and antioxidants that help prevent colorectal cancer. Bring variety to enjoy the widest possible range of beneficial substances they contain (calcium, magnesium, vitamin B9, etc.). A good intake of fruits and vegetables also reduces the risk of many other types of cancer.
    To find out more:
    – Special diet: cancer , recommendations from dietitian Hélène Baribeau;
    -Anti-cancer reflexes on a daily basis , a booklet by David Servan-Schreiber.
  • Limit the consumption of red meat , cold cuts (salami, sausages, smoked ham, etc.) and grilled meat . Those who eat red meat 7 times a week are at risk 85% higher than those who eat only 3 times a week.


Other measures to prevent the onset of the disease

  • Vitamin D . Based on the results of various studies, since 2007, the Canadian Cancer Society has recommended that Canadians take a supplement of 25 μg (1,000 IU) per day of vitamin D in the fall and winter. The organization suggests that people at higher risk of vitamin D deficiency – which includes the elderly, people with dark skin pigmentation, and people who rarely expose themselves to the sun – should do the same. during the whole year. Note that the recommended dosages may vary depending on age and special conditions. For more information, consult our Vitamin D fact sheet.


  • Aspirin . Taking one tablet a day of aspirin (acetylsalicylic acid) may provide some protection. Epidemiological data show that people often taking aspirin are less affected by colorectal cancer. Some contraindications apply because aspirin increases the risk of bleeding.
  • Nonsteroidal anti-inflammatory drugs . In addition to aspirin, other anti-inflammatory drugs may have a protective effect against intestinal polyps and colorectal cancer, such as ibuprofen (Advil, Motrin, etc.) and naproxen (Aleve, Naproxyn, etc.).


Medical treatments for colon cancer

The type of treatment given depends on the stage of cancer progression . The earlier cancer is detected, the better the results.


Surgery is the main treatment. It involves removing the affected part of the colon or rectum , as well as some healthy tissue around the tumor. If the tumor is at an early stage, for example at the polyp stage, it is possible to simply remove these polyps during a colonoscopy .

f the cancer has touched the rectum and a large amount of tissue has had to be removed, a colostomy is performed . This involves creating an artificial anus through a new opening in the abdomen. The faeces are then discharged into an adhesive pocket on the outside of the body.

Preventive surgeries may be performed in people at high risk of colorectal cancer .

Radiation and chemotherapy

These treatments are often necessary to eradicate cancer cells that have already migrated into the lymph nodes or elsewhere in the body. They are most often administered as adjunctive treatments , and are sometimes used as palliative treatment.

The radiation therapy uses different powerful ionizing radiation sources directed at the tumor. It is used before or after the surgery, as the case may be. It can cause diarrhea, bleeding in the rectum, fatigue, loss of appetite and nausea.

The chemotherapy comprises administering, by injection or in the form of tablets, for toxic chemical agents. It can cause several side effects, such as fatigue, nausea and hair loss.


Drugs that limit the proliferation of cancer cells are sometimes used alone or in addition to other treatments. Bevacizumab (Avastin), for example, limits the growth of the tumor by preventing the formation of new blood vessels inside the tumor. It is indicated when the cancer is metastatic.

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