Skip to main content


This information should not be used for self-diagnosis or in place of a qualified physician's care.
Reviewed Dec 2020
The basics
  • Guidelines for treating this cancer have been developed by the Gastrointestinal (GI) Tumour Group.
  • For health professional information on treating this cancer, please see our Cancer Management Guidelines.
  • BC Cancer and BC Cancer Foundation host an educational forum on colorectal cancers every year. Here are video presentations from the 2017 and 2018 Forums.
  • The colon is a part of the bowel, or intestines. The large intestine, which is the lower part of the gastrointestinal tract, consists of the colon and the rectum. The colon is a round tube approximately 2.5 inches (6.4 cm) across and 5-6 feet (1.5–1.8 meters) in length.
    • There are four parts to the colon. It starts where the small intestine ends, at the ileum: then goes up towards the liver (the ascending colon), crosses the abdomen (the transverse colon), goes down the body (the descending colon) and ends at the sigmoid flexure (the s-shaped curve between the descending colon and the rectum).
  • The rectum is about 12 cm long (4.7 inches) and lies between the sigmoid colon and the anal canal.
  • The purpose of the large bowel is to absorb water and eliminate waste for the body.
  • Colorectal cancer is the second leading cause of cancer death in Canada [see note, Statistics].
  • The risk rises with age, especially after age 50.
  • Colorectal cancer occurs more frequently in Canada, the United States, western Europe, Australia and New Zealand, than in Japan, Africa, and developing countries.
  • Cancers of the small intestine or anus are different from colon and rectal cancers.

What causes it and who gets it?

Some of the known risk factors for this cancer are listed below. Not all of the risk factors below may cause this cancer, but they may be contributing factors.

  • Diet may be a factor. Risk seems to increase with diets low in fibre, fruit and vegetables and high in meats and fats. Risk seems to decrease with diets high in fibre and low in fats and red meat / processed meat.
  • What increases the risk of colon and rectal cancers:
    • Polyps or adenomas in the colon may become malignant. Polyps should always be removed and tested to see if they contain cancer. Most polyps do not contain cancer, but if left in place may develop into cancer.
      • One in a hundred patients has a family background of polyps.
      • Gender does not affect the occurence of familial polyposis (Gardner's Syndrome) [see note, Statistics]. Children of an affected parent have a 50% chance of inheriting the syndrome.
  • A family history of colorectal cancer increases risk. The number of relatives affected, and their age when their cancer was diagnosed are important in estimating risk. We have a Hereditary Cancer Program in B.C.
  • People with inflammatory bowel disease (ulcerative colitis, Crohn's disease) have an increased risk of developing colon cancer. This risk increases for patients who developed colitis at an early age.
  • Use of alcohol, especially in men (two (2) or more drinks per day) [see note, Statistics]
  • Body fatness / abdominal fatness
  • Low physical activity levels
  • Rectal cancer can recur (come back) more often than colon cancer. Close follow-up is necessary for these patients, and improves the possibility of cure.
  • Statistics
    NOTE:  Available statistics do not have information about the inclusion of transgender and gender diverse participants. It is unknown how these statistics apply to transgender and gender diverse people.  Patients are advised to speak with their primary care provider or specialists about their individual considerations and recommendations.

Can I help to prevent it?

Research shows that about 50% of colorectal cancers can be prevented by following a healthy lifestyle. This includes:

  • People with moderate to high levels of physical activity have a lower rate of colon and rectal cancers. The evidence of benefit is stronger for colon cancer than for rectal cancer. Visit BC Cancer's Prevention page on Exercise Support for information and resources.
  • Early detection of colon cancer through screening (see below).
  • Eating healthy, nutritious foods can reduce your cancer risk. Follow the recommendations in Canada's Food Guide and cisit BC Cancer's Prevention page on Nutrition information and resources. The following steps may also be helpful for preventing colorectal cancers: 

    - Eat foods high in dietary fibre
    - Include unprocessed garlic in your meals
    - Include milk in your diet
    - If you choose to drink alcohol, the key is to keep your drinking at the safest possible levels, called low-risk drinking.
    - Limit your intake of red meat and processed meat.

Screening for this cancer

  • The provincial Colon Screening Program is an organized population-based program aimed at reducing colon cancer incidence and mortality by promoting the early detection and prevention of colon cancer. 
  • Doctors of B.C. (formerly the B.C. Medical Association) has developed provincial screening guidelines for colon cancer. The patient guideline is available, as well as the health professional guideline.
  • In the general population, screening is recommended to start at age 50. All people aged 50-74 should receive both of these tests:
    • annual digital rectal examination (DRE)
    • a fecal occult blood test, called FIT (Fecal Immunochemical Test). This is a test looking for hidden blood in the feces, that can't be seen with the eye. Fecal occult blood tests can reduce mortality from colorectal cancer by 25% - 45%.
      • The fecal occult blood test is a simple test performed by examining a stool (feces) sample for evidence of bleeding. Unfortunately it does have a high false positive rate for conditions other than cancer, such as: inflammation of the colon, peptic ulcer and hemorrhoids. Even the eating of rare meat or vigorous tooth brushing may produce a false positive result.
      • If you can see blood in your stool, you do not need to do this test. This test is only to check for hidden blood. If you find blood in your stool, contact your doctor.
  • Individuals at higher risk should have more frequent, more thorough examinations beginning at a younger age. The screening guidelines above will help you and your doctor decide on the best plan for you.

Signs and Symptoms

Many of the common symptoms of colorectal cancers could also be caused by other conditions. Consult a doctor for any of the following symptoms.

  • A change in your bowel habits:
    • bowel obstruction
    • stool size change
    • constipation
    • diarrhea
  • Blood in the stool, either apparent (visible) or occult (hidden)
  • Lower abdominal pain or pelvic pain
  • If the tumour has spread, it may result in enlargement of the liver, abdominal bloating, pain in lower back or bladder symptoms such as urinary frequency or blood in the urine.
  • One in twenty patients may develop sudden obstruction of the bowel or a perforation (tear)
  • Anemia
  • Feeling very tired
  • Nausea or vomiting
  • Weight loss and weakness

Diagnosis & staging


These are tests that may be used to diagnose this type of cancer.
  • General physical examination, including a digital rectal examination
  • Routine lab and blood tests
  • Testing of stool sample (feces) for occult (hidden) blood. (also, see Screening above)
  • Barium enema X-ray. A special liquid is inserted into the colon by enema, and then x-rays are taken
  • Sigmoidoscopy – doctors can examine the lowest 50 cm (20 inches) of the colon with a thin, lighted tube. They can also use this scope to grab tiny bits of suspicious looking tissue to put under the microscope
  • Colonoscopy - doctors can examine both the upper and lower colon with a thin, lighted tube. They can also use this scope to grab tiny bits of suspicious looking tissue to put under the microscope
  • Biopsy of colon or rectal tissue. A doctor removes a small portion of the colon or rectum to examine under a microscope. This is the most accurate test of all, but because it involves cutting the body, the other less invasive tests are usually done first.
  • CT scan of abdomen and pelvis
  • Ultrasound of abdomen
For more information on tests used to diagnose cancer, see our Recommended Websites, Diagnostic Tests section.

Types and Stages

  • Most cases of bowel and rectal cancers are adenocarcinomas
  • Sometimes a lymphoma or melanoma, sarcoma or squamous cell carcinoma may be found
  • Cancer of the small intestine (not the colon or rectum) is different, as is anus cancer.
Staging describes the extent of a cancer. The TNM classification system is used as the standard around the world. In general a lower number in each category means a better prognosis. The stage of the cancer is used to plan the treatment.

T describes the site and size of the main tumour (primary)

N describes involvement of lymph nodes

M relates to whether the cancer has spread (presence or absence of distant metastases)

Stage I
Cancer is only in the bowel wall, not penetrating the muscle in the wall. The cure rate exceeds 90%

Stage II
Lesions (an area of abnormal tissue) which penetrates muscle into the surrounding fat. The cure rate is about 70%

Stage III
Regional lymph node involvement is demonstrated. Likelihood of cure is about 50%, depending on the number of lymph nodes involved

Stage IV
Patient has metastatic disease (the cancer has moved to other areas) or the tumour has grown and spread into other organs. The cancer is often incurable at this point, although there are treatments that can relieve symptoms, improve the quality of life and significantly extend life.



Cancer therapies can be highly individualized – your treatment may differ from what is described below. Colon and rectal cancers are sometimes treated differently, so they are listed separately here.

Colon Cancer

Treatment options depend on where the tumour is in the colon, how big it is and if it has grown or spread outside of the original site.

  • Surgery is the best option for a cure. The main aim of surgery is to cut out the cancer with a wide border above and below the tumour, as well as the lymph nodes near to the tumour.
  • If a cure is not possible, tumours should still be removed to prevent possible blockage of the bowel or bleeding.
  • In most cases the bowel can be rejoined during surgery: this is called anastomosis. Anastomosis (connecting) is sometimes not possible for patients who have obstructing tumours in the left (descending) side of the colon. Instead, they receive a colostomy. A colostomy is an opening in the abdomen that allows stool to empty into a plastic pouch attached over the opening. Usually a colostomy is temporary and the bowel may be re-anastomosed at a later date.
  • If the tumour comes back as a single spot of tumour found in the lung or liver, occasionally it may be surgically removed.


  • Radiotherapy isn't usually useful in colon cancer.
  • Sometimes it is used to relieve symptoms when cure is not possible.


  • Chemotherapy may be given after surgery for patients who are at higher risk of relapse (recurrence). There are various chemotherapy combinations that may be offered, depending on individual circumstances.

Rectal Cancer

Treatment options depend on where the tumour is in the rectum, how big it is and if it has grown or spread outside of the original site.


  • If the cancer is in the rectum, there are different kinds of surgery that may be performed. The type of surgery usually depends on how high up the rectum the cancer is located.
  • Most rectal cancer surgeries will require creation of a temporary or permanent colostomy
  • Colostomy - the surgeon may create an artificial anus on the abdominal wall by cutting the colon and bringing the ends out to the surface. A pouch is worn over the hole (a stoma) to collect the waste.
  • Very low rectal tumours (near the outside of the body) may require removal of the entire rectum with a permanent colostomy.
  • For operable rectal cancers, chemotherapy and radiation may assist in improving the chance for cure.
  • Inoperable rectal tumours may be treated with radiation therapy or combined chemotherapy/radiation. 


  • Radiation therapy may be given before or after surgery.
  • Recurrent rectal cancer may be controlled with radiation and chemotherapy.


  • Chemotherapy may be given before or after surgery for patients who are at higher risk for recurrence.
  • Chemotherapy can be given alone or combined with radiotherapy.

Follow-up after Treatment

  • Guidelines for follow-up after treatment for colon cancers are covered on our website. 
  • Guidelines for follow-up after treatment for rectal cancers are covered on our website.
  • You will be returned to the care of your family doctor or specialist for regular follow-up. If you do not have a family physician, please discuss this with your BC Cancer oncologist or nurse.
  • Follow-up testing is based on your type of cancer and your individual circumstances.
  • Life after Cancer focuses on the issues that cancer survivors can face.
Tab Heading
SOURCE: Colorectal ( )
Page printed: . Unofficial document if printed. Please refer to SOURCE for latest information.

Copyright © BC Cancer. All Rights Reserved.

    Copyright © 2021 Provincial Health Services Authority