Colorectal Cancer Screening

This is the third most common cancer diagnosed in both men and women in the United States.  The overall lifetime risk of developing colorectal cancer is about 1:23, that is 4.4% for men and 1:25, that is 4.1% for women.

Many lifestyle related factors have been linked to colorectal cancer.  In fact, the links between diet, weight and exercise and colorectal cancer risk are some of the strongest for any type of cancer.  Being overweight raises the risk of colon and rectal cancer in both men and women, but the link appears to be stronger in men so getting and staying at a healthy weight will help lower your risk.  If you are not physically active, you have a greater chance of developing colon cancer.  Regular, moderate to vigorous physical activity can help lower your risk.


Diets which are high in red meats and processed meats raise the colorectal cancer risk.  Cooking meats at very high temperatures (frying/boiling or grilling) creates chemicals that might raise your cancer risk.  However, it is not clear how much this increases the colorectal cancer risk. 

It is also thought that a low blood level of vitamin D may also increase your risk.  It is therefore suggested that following a healthy eating pattern that includes plenty of fruits, vegetables and whole grains and which limits or avoids red or processed meats and sugary drinks probably lowers the risk. 


Smokers or people who have smoked tobacco for a long time are more likely than non-smokers to develop and die from colorectal cancer. Clearly, smoking is a well known cause of lung cancer but it is also linked to other cancers.  If you smoke, then it is suggested that you quit. 

Heavy alcohol risk

Colorectal cancer has been linked to moderate to heavy alcohol use.  It is best to not drink alcohol.  If you do then alcohol consumption should be limited to no more than two drinks a day for men and one drink a day for women.  These are all risk factors which you can change.  However, there are colorectal cancer risk factors which you cannot change. 


The risk of colorectal cancer goes up with age.  It is much more common after the age of 50. 

Personal history of colorectal polyps or colorectal cancer

If there is a history of adenomas, then there is an increased risk of developing colorectal cancer.  This is especially true if polyps are large or if there are many of them or if they show dysplasia.  If you have a previous history of colorectal cancer, even if it was completely removed, then you are more likely to develop new cancers in other parts of the colon or rectum.  The chances of this happening are greater if you had your first colorectal cancer when you were young.

History of inflammatory bowel disease

If there is a history of inflammatory bowel disease including ulcerative colitis or Crohn’s then there is an increased risk of colorectal cancer.  Inflammatory bowel disease is a condition in which the colon is inflamed over a long period of time.  People who have had inflammatory bowel disease for many years, especially if untreated, often develop dysplasia.  Dysplasia is a term used to describe the cells in the lining of the colon or rectum that look abnormal, that are not true cancer cells.  They can change into cancer over time.  In these circumstances, screening for colorectal cancer is offered earlier.  It should be noted that irritable bowel syndrome does not increase the risk for colorectal cancer.

Family history of colorectal cancer or adenomatous polyps

Most colorectal cancers are found in people without a family history of colorectal cancer.  Still, nearly one in three people who develop cancer have other family members who have had it.

People with a history of colorectal cancer in a first-degree relative, that is parent, sibling or child are at an increased risk.  The risk is even higher if that relative was diagnosed with cancer when they were younger than 45, or if more than one first-degree relative is affected. 

The reasons for this increased risk is not clear in all cases.  Cancers run in families because of inherited genes, shared environmental factors or a combination of both. 

Having family members who have had adenomatous polyps is also linked to a higher risk of colon cancer.  In these cases, early screening is advised. 

Inherited syndromes

5% of people who develop colorectal cancer have inherited gene changes, mutations that cause family cancer syndromes and can lead to them getting the disease.  The most common inherited syndromes linked with colorectal cancers are Lynch syndrome and familial adenomatous polyposis. Other syndromes include Peutz-Jeghers syndrome where patients tend to have freckles around the mouth and sometimes in the hands and feet and a special type of polyp called hamartomas in their digestive tract.  These patients are also at a much higher risk for colorectal cancer.

MYH-associated polyposis

People with this syndrome develop many colon polyps.  They also have a higher risk of other cancers of the gastrointestinal tract and thyroid.

Racial and ethnic background

Jewish patients of Eastern European descent, Ashkenazi Jews, have one of the highest colorectal cancer risk of any ethnic group in the world.  This could be related to the increased incidence of the BRCA 1 and 2 genes.

African Americans have the highest colorectal cancer incidence and mortality of all racial groups in the United States.  The reasons for this are not fully understood. 

Factors with unclear effects on colorectal cancer risk

Night shift work.  Studies have shown that working a night shift on a regular basis may increase the risk of colorectal cancer.  It is thought that this may be due to changes in the level of melatonin, a hormone which responds to changes in light.  More research is required. 

Previous treatment for certain cancers

Some studies have shown that men who survived testicular cancer seem to have a higher rate of colorectal cancer and some other cancers and this may be related to the treatments they received such as radiation therapy.  Patients who have also had radiotherapy for prostate cancer might have a higher risk of rectal cancer because the rectum receives some radiation during treatment.  This, however, is based on studies when patients were treated in the 1980s and 1990s when radiation treatments were much less precise than they are today.

So, can colorectal cancer be prevented?

There is no definitive way to prevent colorectal cancer but clearly there are investigations to reduce the risk.  Risk factors have been mentioned above and if you fall within one of these then you can take action. 

Colorectal cancer screening

Regular colorectal cancer screening is one of the most powerful tools for preventing colorectal cancer.  From the time the first abnormal cells start to grow into polyps, it usually takes about 10 to 15 years for them to develop into colorectal cancer.

With regular screening, most polyps can be found and removed before they have the chance to turn into cancer.  Screening can also find colorectal cancer early when it is small and easier to treat. 

So, what is recommended?

Colorectal screening should be offered to asymptomatic patients over the age of 45 if

an average risk of colorectal cancer.

Under the age of 45, if an increased risk of colorectal cancer or having symptoms potentially attributable to colorectal cancer. 

Higher risk therefore includes:

  • A personal history of colorectal cancer or polyps.
  • History of inflammatory bowel disorder
  • Family history of colorectal cancer or polyps, particularly if affected younger relatives under the age of 50.
  • Family history of hereditary colorectal cancer syndrome such as Lynch syndrome etc. 

Referral should also be considered to a clinical geneticist for anyone with a family history of young first degree relatives with colorectal cancer. 

How is one screened?

CT colonography either with or without intravenously administered contrast.  This is undertaken with a low-dose CT radiation scan prior to which the patient will have been asked to clear their bowel with the use of laxatives.  The advantage of this scan is that it also shows extracolonic organs and at the same time a CT scan of the chest if required or CT coronary calcium score can be undertaken.  The disadvantages are that if a polyp is found, this will require a further referral for traditional colonoscopy.


A traditional method where a fiberoptic telescope is inserted through the anus with prior bowel preparation with laxatives.  The advantages are that any polyps can be removed at the time, but no other organs are visualised. 

FIT test

This is a faecal immunochemical test which will highlight whether any blood is present in the stool which might be indicative of a rectal/colonic lesion.  This is not a very accurate assessment and should in no way be utilised as an alternative to CT colonography or colonoscopy.  A FIT test can be performed annually or two years post colonoscopy or CT colonography. 
CT colonography/colonoscopy is recommended every five years subject to a negative initial test. 

Symptomatic patients of any age should be referred to a gastroenterologist or colorectal surgeon.  Symptoms include any change in bowel habit, blood in the stool, abdominal pain, discomfort or bloating.

Reiterating how can one self-help to reduce the risk of colorectal cancer

  1. Staying at a healthy weight may help to lower risk.
  1. Physical activity.  Increasing the intensity and amount of physical activity may help to reduce risk. 
  1. Diet.  Limiting red and processed meats and eating more vegetables and fruits may help lower risk.
  2. Alcohol.          Avoiding alcohol may help to reduce risk.
  1. Cessation of smoking.
  1. Vitamins, calcium and magnesium. Studies have shown that taking a daily multivitamin containing folic acid may lower colorectal cancer risk.  This, however, is controversial as some studies have hinted that folic acid may help existing tumours to grow.  More research is needed.  Studies have also suggested that vitamin D might lower colorectal cancer risk.  However, as vitamin D is provided by sun exposure, this has not been recommended as a way to lower colorectal cancer currently.  There have also been other studies showing that low blood vessels of vitamin D do increase risk.  It is suggested that vitamin D levels should be monitored and supplemented by oral medication as required.

Low levels of dietary calcium have been linked with an increased risk of colorectal cancer in some studies.  Other studies have also shown that increasing calcium intake may lower colorectal cancer risk.  However, there is an association with increased calcium with prostate cancer.  Currently, further studies are recommended in order to be able to provide the appropriate advice.

Calcium and vitamin D probably work together to reduce colorectal cancer risk.

Magnesium.  Some studies have suggested that a diet high in magnesium reduces colorectal cancer.  Again, more research is required.

  1. Non-steroidal anti-inflammatory drugs.     Many studies have shown that people who regularly take aspirin or other non-steroidal anti-inflammatory medications such as ibuprofen have a lower risk of colorectal cancer and polyps.  However, aspirin and non-steroidals can cause serious or even life-threatening side effects such as bleeding from the intestine and these can outweigh the benefits of taking medicines.  At this stage, there is no specific recommendation to take non-steroidal anti-inflammatories in order to lower colorectal cancer risk.
  1. Hormone replacement therapy.  Studies have shown that taking oestrogen and progesterone after the menopause may reduce a woman’s risk of developing colorectal cancer.  However, cancers found in these women appear to show that they are at a more advanced stage.  There also the effects of taking hormones which increase the risk of cardiovascular disease, blood clots and cancers of the breast and lung and therefore HRT is not recommended as an aid to lowering colorectal cancer risk.

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