Primary prevention of cancer is an important objective and there is a need to focus on this vital factor as much as on secondary prevention. The interesting statistics on the 5-year survival rate for specific cancers are shown in Table 9.3 .
That environmental factors are involved in the aetiology of colorectal cancer and other cancers is indicated by wide variations in incidence between different countries.
Suspicion falls on diet and there is epidemiological evidence implicating diets high in animal fats and low in insoluble fibre, fruits and vegetables, and also high alcohol consumption. It is noted that there are higher incidence rates in people migrating from low- to high-risk countries, e.g. Japanese to Hawaii 5 and Greeks and Italians to Australia. 6
Studies in the United States indicate that at least 35% of all cancer deaths are related to diet. Obese individuals have increased risk of colon, breast and uterine cancers. High-fat diets are a risk factor for prostate, breast and colon cancers. Salt-cured, smoked and nitrate-cured foods increase the risk of upper GI cancers. Foods rich in vitamin A and folate (dark green and deep yellow vegetables and fruits) and vitamin C and cruciferous vegetables (cabbage, brussels sprouts, broccoli and cauliflower) are all considered to have protective effects for various cancers. 7 Photochemicals (plant chemicals) exist in these foods and in other vegetables and fruit that have a cancer-protective effect. 8 Overall, diet, smoking, alcohol and occupational exposures (5%) appear to account for over 73% of all cancer mortality. 7
Doll and Peto 9 consider that environmental factors are responsible for 80-90% of cancers and estimate that diet is a major factor in the cause of cancer in 40% of men and 60% of women.
Table 9.3 Cancer prognosis: 5-year survival
USA (whites) 1960-63 1983-88
Lung 8 13
Bowel 40 58
Australia South Australia
10 12 35 55
Source: Statistics provided by Dr Graham Giles, Anti Cancer Council of Victoria
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