Colorectal cancer was the second most common cancer in Ireland. It accounted for 13% of all malignant neoplasms, excluding non-melanoma skin cancer, in women and 15% in men (Table 5.1). The annual average number of new cases diagnosed was 1,307 in women and 1,631 in men. 63% of these cancers arose in the colon and 37% in the rectum. During 1995-2007, the number of new cases increased, on average, by approximately 2% per annum, but during 2002-2007 increased by 4% per annum. The patterns of increase were similar for RoI and NI.

The risk of developing colorectal cancer up to the age of 74 was 1 in 32 for women and 1 in 20 for men and was similar for NI and RoI. At the end of 2008, 2,335 women and 2,787 men aged under 65, and 6,137 women and 7,205 men aged 65 and over, were alive up to 15 years after their colorectal cancer diagnosis.

Table 5.1 Summary information for colorectal cancer in Ireland, 1995-2007

Approximately half of colorectal cancers were diagnosed in those aged 70 and older—51% of men and 58% of women (Figure 5.1). The age distribution was similar for both sexes, although there was a higher proportion of cases in men aged 60–69 (29%, compared to 22% in women) and a higher proportion in women aged 80 and older (26%, compared to 17% in men).

Figure 5.1 Age distribution of colorectal cancer cases in Ireland, 1995-2007, by sex

The incidence of colorectal cancer among both men and women in RoI and NI was close to the median for the countries shown. Rates were highest in New Zealand among women and in the Czech Republic for men (Figure 5.2).

Figure 5.2 Estimated incidence rate per 100,000 in 2008 for selected developed countries compared to 2005-2007 incidence rate for RoI and NI: colorectal cancer
females	males
Source: GLOBOCAN 2008 (Ferlay et al., 2008) (excluding RoI and NI data, which is derived from cancer registry data for 2005-2007)

Table 5.2 Risk factors for colorectal cancer, by direction of association and strength of evidence

Up to 10% of colorectal cancers are hereditary and most are due to the genetic syndromes of familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) (Hawkins and Ward, 2001). Excluding these syndromes, individuals who have a first degree relative with colorectal cancer have around a two-fold increased risk of developing the disease themselves.

Lifestyle factors are extremely important in colorectal cancer (Table 5.2). Smoking is causally related to colon, but not rectal, cancer. Alcohol is a cause of both colon and rectal cancers. Higher levels of body fatness, and in particular central adiposity, are positively related to risk. In a recent meta-analysis, each 5kg/m² increment in body mass index was associated with an 18% increase in risk; the association appears stronger for colon than rectal cancer, for men than women, and in studies adjusting for physical activity (Ning et al., 2010). In contrast, physical activity is consistently inversely associated with colon cancer, in particular, and risk decreases in a dose-response fashion with increased frequency or intensity of activity. Regular use of aspirin or other non-steroidal anti-inflammatory drugs may reduce colorectal cancer risk by up to half. In addition, risk is decreased in women taking hormone replacement therapy and is likely also to be lower in those who have taken oral contraceptives.

Many studies have found increased risk in individuals who have higher intakes of processed meats (preserved by smoking, curing or salting, such as ham, bacon or salami) and red meats. In contrast, higher intake of various other dietary components may be associated with lower risk, including garlic; fruit; fish; non-starchy vegetables; milk, dairy products or calcium; coffee; soya and soya foods; and foods containing dietary fibre or the B vitamin folate.

Map 5.1 Colorectal cancer, smoothed relative risks: both sexes

Map 5.2 Colorectal cancer, smoothed relative risks: males

Map 5.3 Colorectal cancer, smoothed relative risks: females