Colorectal cancer

Colorectal cancer

Colorectal cancer affects the large bowel, colon and rectum. It is one of the most common adult cancers, and can usually be treated if caught early on.

The risk of developing colorectal cancer increases from the age of 40; 90% of these cancers will occur in people over 50. In about 30% of cases, it is an inherited condition.

Most colorectal cancers develop from polyps – growths that look like tiny mushrooms – in the colon. Polyps are common, especially after the age of 50, and not all will develop into cancer.


Colorectal cancer is slow-growing: it takes 10-15 years for polyps to become cancerous, and a tumour may be present for as long as five years before symptoms appear. These symptoms can be so slight that they are ignored.

Symptoms depend on where the cancer is. When the tumour grows, it can obstruct the bowel, or grow into the pelvic bones and cause local pain. The patient may feel abdominal pain after meals or have changed bowel habits. The left side of the colon is narrower that the right, so tumours on that side can cause greater obstruction.

A patient may notice blood in the stool (red or tarry in colour). Red blood is caused by cancers low down, in or near the rectum. The bleeding is not constant, and many sufferers assume it is due to haemorrhoids (piles). Colorectal cancer is also often misdiagnosed as irritable bowel syndrome (“spastic colon”) or diverticular disease.

Other common symptoms are:

  • Foul-smelling stool
  • Abdominal discomfort such as colic, bloating or fullness
  • Fatigue
  • Weight loss
  • A feeling that one wants to pass stool, but nothing comes out


Any abdominal symptoms should be fully investigated, and all patients with blood in their stool should have a colonoscopy. The procedure involves passing a lighted tube through the anus into the rectum and lower colon, so that your doctor can see any polyps or cancer present. If a growth is found, it (or a piece of it) can be removed and sent to the pathologist for evaluation.

Other methods to test for cancer include:

  • Testing for blood or genetic material in the stool
  • Capsule endoscopy. The patient swallows a tiny camera that takes pictures of the bowel.
  • CT colonography. The radiologist constructs a 3D image of the bowel. This procedure is non-invasive, but patients receive a dose of radiation.
  • CD24 and CEA tests. These blood tests detect protein levels that are higher in the presence of particular cancers. The CD24 test can also detect growths that are destined to become cancerous.


Treatment will depend on where the cancer is and how far it has progressed. Most people will need an operation or stent. With successful surgery, a cancer may be removed completely. However,

if the cancer is too far advanced for this cure, an operation will still be necessary to relieve any obstruction or bleeding the cancer may cause.

A stent is an expandable “spring” that can be put into the colon via a colonoscope (without an operation) as a temporary measure to relieve obstruction.

A colostomy (the so-called bag) is only necessary if the cancer is very low in the rectum.

For more advanced cancers, chemotherapy will be administered within eight weeks following surgery. Some patients may receive radiation therapy before and after surgery.


Many factors influence the patient’s chances of recovery, such as how far the cancer cells have developed, if blood vessels are involved, how deep the cancer has penetrated into the bowel, etc.

The outlook for the patient may be improved if:

  • The patient had no symptoms.
  • Rectal bleeding was present.
  • The cancer was in the colon (rather than rectum).
  • The cancer was left-sided rather than right-sided.

A poor prognosis may be suggested if:

  • The patient is under the age of 30.
  • The patient had high levels of CEA (carcinoembryonic antigen) before the operation.
  • The cancer has spread to other areas.
  • A bowel obstruction or perforation was present.

Following surgical removal of a cancer, lifelong follow-up will be needed to check that the cancer has not recurred or spread to other organs. Two to three years later, the chances of the cancer recurring are slim, but surveillance is still necessary as new polyps might develop.


The earlier cancer, or potential cancer, can be detected, the better. Everyone should have a colonoscopy to screen for polyps at the age of 50, and after that every 10 years.

Relatives of a colorectal cancer patient should start screening 10 years before the age at which their family member was diagnosed, or at 40 – whichever comes first. (Eg. if your father was diagnosed at 40, you and your siblings should start testing at 30 years.) People with inflammatory bowel disease (eg. Crohn’s disease or ulcerative colitis) and their families are also at higher risk.

Some inherited forms of colorectal cancer need earlier surveillance. In familial adenomatous polyposis, thousands of polyps develop in the large bowel. Most people with this condition will die before 40 if they are not screened from 10 to 12 years of age and treated. If many members of your family have various forms of cancer, screening should start in your early twenties and be repeated every year or two.

Genetic testing can establish if you have certain inherited conditions that increase risk.


In addition to screening, we can modify our behavior to lower risk. As many as 70% of colorectal cancers can be prevented through moderate changes in lifestyle.

High alcohol intake is associated with rectal cancer. Smoking also increases risk – especially if you smoke more than 40 cigarettes per day, started smoking early in life or have smoked for a long time.

Body mass index (BMI: weight in kg divided by the square of height in metres) plays a significant role in colon cancer. Above a healthy weight, the greater the BMI, the greater the risk. Those with a BMI of 30 and higher have a 41% increased risk. Men have a higher risk than women if their waist circumference increases. This may be related to higher insulin levels in obese people.

Physical activity:  Moderate physical activity (such as brisk walking 3-4 hours per week) can reduce your risk by 20-30%. This could be because exercising reduces abdominal fat, inflammation and insulin levels. (Insulin may increase growth factors in the body, which promote cancer.)

Diet:  A typically “Western” diet consisting of large amounts of red meat and highly refined carbohydrates is associated with an increased risk of colorectal cancer. This may be related to the levels of insulin or inflammation. However:

  • It has not been shown that a high-fibre diet lowers the risk of colorectal cancer. However, many people who eat a high-fibre diet also follow a generally healthy lifestyle and consume other nutrients with anti-cancer effects.
  • While eating red meat is associated with colorectal cancer, the culprit is not meat itself but the way it’s cooked. Meat with a heavily browned surface, or that has been prepared at prolonged high temperatures, increases risk.
  • Other sources of animal protein (dairy products, fish and poultry) are associated with reduced risk.
  • Calcium intake can reduce the risk of developing polyps and colorectal cancer. The intake should be 700-800 mg per day: higher doses are not beneficial.
  • The benefits of calcium appear to be limited to people with higher vitamin D levels. Calcium and vitamin D are found in cod-liver oil, cereals, milk and milk products. Sun exposure helps to form vitamin D in the skin.
  • Vitamin B9 (folate) may prevent the formation of polyps and cancer. Dietary folate is better than the synthetic form (folic acid) in supplements. (However, extra folate may aggravate existing growths.) It requires more that 10 years of extra folate intake before it becomes beneficial.
  • A higher intake of vitamin B6 (pyridoxine) may reduce in colorectal cancer, especially in those who drink a lot of alcohol.

Medications: Patients who have had colorectal cancers removed may benefit from using aspirin and certain other painkillers, which reduce mortality. They also reduce polyps in patients with familial andenomatous polyposis. Postmenopausal hormone therapy may lower risk for colorectal cancer.

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