Screening for Colorectal Cancer

Colorectal cancer is the third most common cancer and cause of cancer related death worldwide. The majority of people developing colorectal cancer have no predisposing factor, but up to 20% may have a genetic predisposition. Survival is strongly related to the stage of the disease at diagnosis. Where the cancer is locally confined, survival of over 90% has been reported. Randomised controlled trials have shown that screening programmes for colorectal cancer reduces death from this disease.

Almost all cancers of the colon and rectum develop from a pre-malignant polyp. This polyp undergoes certain genetic changes and over time, can into an invasive cancer. Even invasive cancers may have no symptoms and when it becomes symptomatic, the disease may be in an advanced stage. Screening is aimed at detecting pre-malignant polyps or early, asymptomatic cancers.

The average risk person has about a 5% chance of developing colorectal cancer. People of average risk is defined as someone over the age of 50, with no other risk factors for developing colorectal cancer. People with a first- or second degree relative who developed colorectal cancer over the age of 60 years, are also at average risk.

High risk individuals are those who have a strong family history of colorectal cancer. This includes people with a first degree relative who was diagnosed with colorectal cancer younger than 60, or those who have 2 or more first degree relatives with colorectal cancer.

There are a few methods for screening. Faecal occult blood testing, flexible sigmoidoscopy and colonoscopy are the 3 modalities used. Of these screening tools, colonoscopy is the most accurate and is advocated by the American College of Gastroenterology as the screening method of choice.

When should I go for a screening colonoscopy?

If you have no family member who had colorectal cancer, or one of your immediate family members was diagnosed with colorectal cancer older than 60 years of age, you should have a colonoscopy at ages 50, 60 and 70.

If you have a strong family history of colorectal cancer, it is advised that you speak to your doctor to help you with when you should go for a screening colonoscopy.