Recommendations for reducing the risk of colorectal cancer include:

• completing the National Bowel Cancer Screening Program (NBCSP) at-home bowel cancer test every two years if aged 50–74 years
• eating a healthy diet, including plenty of vegetables, fruit and whole grains while minimising intake of red meat, barbequed/grilled meat and processed meat
• maintaining a healthy body weight
• undertaking regular physical activity
• avoiding or limiting alcohol intake
• not smoking.

For all people aged 50–70 years, including those at average risk of colorectal cancer, aspirin should be actively considered to prevent colorectal cancer, in conjunction with other comorbidities. A low dose (100–300 mg per day) is recommended for at least 2.5 years (Cancer Council Australia Colorectal Cancer Guidelines Working Party 2019). Benefit for cancer prevention (though shorter for cardiovascular risk) is evident only 10 years after initiation, so a life expectancy of at least 10 years should be taken into consideration in the advice to use aspirin (Cancer Council Australia Colorectal Cancer Guidelines Working Party 2019).

Based on family history, people can be placed into one of three categories (described below) of relative risk of developing colorectal cancer. Age is an independent risk factor for colorectal cancer. These categories were developed by the Cancer Council Australia Colorectal Cancer Guidelines Working Party (2019).

General practitioners and primary care nurses should educate patients and encourage them to participate in the screening appropriate to the patient’s level of risk.

Category 1: Near average risk

Risk factors for category 1 patients include:

• no first- or second-degree relative with colorectal cancer
• one first-degree relative with colorectal cancer diagnosed before the age of 55
• one first-degree and one second-degree relative with colorectal cancer diagnosed at 55 years or older.

People who have one relative with colorectal cancer diagnosed at age 55 or older should be advised that their own risk of developing colorectal cancer could be up to twice the average risk but is still not high enough to justify colorectal cancer screening by colonoscopy.

Category 2: Moderately increased risk

People in this category should be advised that their risk of developing colorectal cancer is at least three times higher than average but could be up to six times higher than average, if they have any of the following:

• one first-degree relative with colorectal cancer diagnosed before the age of 55
• two first-degree relatives with colorectal cancer at any age
• one first-degree relative and at least two second-degree relatives diagnosed with colorectal cancer at any age.

Category 3: High risk

People in this category should be advised that their risk of colorectal cancer is at least seven times higher than average but could be up to 10 times higher than average, if any of the following apply:

• at least three first-degree relatives diagnosed with colorectal cancer at any age
• at least three first-degree or second-degree relatives with colorectal cancer, with at least one diagnosed before age 55 years
• they are a member of a family in which a gene mutation that confers a high risk of bowel cancer has been identified.

The NBCSP invites people starting at age 50 and continuing to age 74 (at average risk and asymptomatic) to screen for bowel cancer using a free, simple test at home.

NBCSP participants with screen-detected bowel cancer are more likely to be diagnosed at a less advanced stage than those who did not participate (Cancer Council Australia 2020). NBCSP participants with screen-detected bowel cancer had a lower risk of bowel cancer mortality compared with those who were diagnosed outside of the program (9.6 per cent vs 23.8 per cent) (AIHW 2018b). Bowel cancer screening on a population basis significantly reduces mortality and morbidity (Cancer Council Australia 2020).