Colorectal cancer, also known as bowel cancer, colon cancer or rectal cancer, starts in the cells of the colon or rectum – parts of the large intestine and the digestive system. Most colorectal cancers first develop as polyps, which are abnormal growths inside the colon or rectum that may become cancerous if they’re not removed. Although not all polyps develop into cancer, colorectal cancer almost always develops from a polyp.
Colorectal cancer is the third most commonly diagnosed cancer in Canada. It is the second leading cause of cancer death in men and the third leading cause of cancer death in women. However, when discovered early, it is highly treatable.
The Canadian Cancer Society estimates that: about 1 in 14 Canadian men will develop colorectal during their lifetime and 1 in 32 will die from it; about 1 in 18 Canadian women will develop colorectal cancer during their lifetime and 1 in 37 will die from it.
Incidence rates on the decline in people over 50
Most people diagnosed with colorectal cancer are over the age of 50, and the risk increases with age. Fortunately, the incidence rates of colorectal cancers in both women and men are declining, as are the rates of death. This is likely due in part to increased use of colorectal cancer screening and improved diagnosis and treatment. Surprisingly though, studies recently published in the U.S. and Canada have found that while the rates are on the decline in older people, they’re on the rise in millennials (born 1981-1996) and Gen-Xers (born 1965-1980).
The Canadian Cancer Society confirmed this trend and reported that 7% of all colorectal cancers in Canada were diagnosed in people under 50. Researchers think this is the result of lifestyle factors rather than genetics. Lifestyle risk factors for cancer include excess weight, lack of exercise, poor eating habits, alcohol consumption and smoking.
Risk factors for colorectal cancer
It’s not clear exactly why colorectal cancer develops in some people and not others. Risk factors increase the chances of developing cancer but sometimes colorectal cancer develops in people without any of the identified risk factors. Risk factors include:
- Age: Colorectal cancer is more common in people over age 50, and the chance of developing colorectal cancer increases with each decade.
- Personal history of colorectal polyps:Polyps are non-cancerous growths on the inner wall of the colon or rectum. While fairly common in people over 50, one type of polyp, called an adenoma, increases the risk of developing colorectal cancer.
- Personal history of colorectal cancer:Someone who has already had colorectal cancer may develop the disease a second time in other areas of the colon or rectum. The chances are greater if the first occurrence was at an age younger than 50.
- Personal history of inflammatory bowel disease (IBD): Inflammatory diseases of the colon, such as Ulcerative Colitis and Crohn’s Disease, can increase the risk of colon cancer.
- Family history of colorectal cancer: First degree relatives (parents, siblings, children) of someone who has had colorectal cancer are somewhat more likely to develop colorectal cancer, especially if the relative had the cancer at a young age.
- Ashkenazi Jewish ancestry: Jewish people of Eastern European descent have a higher than average risk of developing colorectal cancer. This group tends to have a specific mutation in the APC gene that increases the risk.
- Personal history of other cancers: Research shows that women with a history of ovarian, uterine, endometrial or breast cancer have a somewhat increased risk of developing colorectal cancer.
- Type 2 Diabetes: People with type 2 (usually non-insulin dependent) diabetes may have an increased risk of developing colorectal cancer.
- Diet: Colorectal cancer appears to be associated with diets high in fat and calories, red and processed meats and low in fibre, vegetables and fruits. Researchers have also suggested that methods of cooking meats at very high temperatures (frying, broiling or barbecuing) create chemicals that might increase cancer risk.
- Sedentary lifestyle/physical inactivity: People who are not physically active are more likely to develop colorectal cancer. Higher amounts of sedentary behaviour (sitting for long periods of time) are linked to a higher risk for colorectal cancer, particularly cancer in the distal colon and rectum.
- Obesity: People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer.
- Smoking: Long-term smokers are more likely than non-smokers to develop and die from colorectal cancer. While smoking is a well-known cause of lung cancer, some of the cancer-causing substances are swallowed and can cause digestive system cancers, such as colorectal cancer.
- Highalcohol consumption: Colorectal cancer has been linked to the heavy use of alcohol. Alcohol use should be limited to no more than 2 drinks per day for men and 1 drink per day for women.
- Genetic conditions: Rare genetic syndromes can increase the risk of developing colon cancer. The two most commonly inherited syndromes linked with colorectal cancers are: Familial adenomatous polyposis (FAP) and Lynch syndrome, also called hereditary non-polyposis colorectal cancer (HNPCC).
Symptoms of colorectal cancer
Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they usually vary, depending on the cancer’s size and location in the large intestine.
Signs and symptoms of colon cancer include:
- a persistent change in bowel habits, including diarrhea or constipation or a change in stool consistency
- rectal bleeding or blood in the stool
- persistent abdominal discomfort, such as cramps, gas or pain
- a feeling that the bowel doesn’t empty completely
- weakness or fatigue
- unexplained weight loss
Most of these symptoms may also indicate other possible conditions. It’s important to see a health care professional if symptoms persist for 4 weeks or more.
Preventing colorectal cancer
There are some risk factors for colorectal cancer that you can’t control, however, you can make changes to your lifestyle. Exercising, maintaining a healthy body weight and eating plenty of fibre, fruit and vegetables and minimizing red and processed meats can help reduce the risk.
If you are between the ages of 50 and 74, the Canadian Cancer Society strongly recommends you speak to your health care professional about screening or contact your provincial colorectal cancer screening program. If you do not have any symptoms, regular screening for colorectal cancer is recommended every 2 years for average-risk adults aged 50 to 74. Screening can detect polyps so they can be removed before they become cancerous. It can also detect colon cancer during its early stages when the chances of successful treatment are much higher. Adults 75 and over should discuss the benefits of screening with their health care professional.
If you are at higher risk for colorectal cancer, speak to your health care professional about what screening options are best for you.
The most common screening test for colorectal cancer is a blood stool test called a fecal occult blood test. This checks a sample of stool for the presence of blood. It can be done at the doctor’s office or with a kit at home and the sample is sent to a lab for testing.
Polyps or tumours in the colon have blood vessels that can release a small amount of blood onto the stool. Stool tests check for this hidden blood, which you can’t see with your eyes. Having blood in your stool doesn’t always mean you have polyps or cancer. If a stool test shows traces of blood, more tests need to be done to find out where the bleeding is coming from and why.
Speak to your health care professional about the benefits and risks of screening for colorectal cancer.