Epidemiology of Cancer

Question 1

Compare the change in mortality rate of CVDs and cancers in western countries

Answer 1

after the 60s

• drop in mortality from CVDs - rapid drop in heart diseases
• cancer mortality remained constant
• In high-income countries, mortality from cancer IS decreasing, so death rates from cancer overall are decreasing. Low-income countries have a completely different pattern

Question 2

Why must we distinguish between mortality and incidence?

Answer 2

incidence is to do with the number of new cases diagnosed, irrespective of death this includes BENIGN tumours that will not lead to death, but contributes to incidence. There are high incidence rates for certain cancers that have low mortality rates. Other cancers exist where mortality and incidence rates are similar (e.g. pancreatic cancer)

• Mortality rates are affected by many things (e.g. access to healthcare, effectiveness of therapy) whereas incidence rates reflect causality – they reflect risk factors and lifestyle

Question 3

What are the main cancers in men and women?

Answer 3

men = prostate and lung

women = breast

Question 4

What is the geographical variation of melanoma?

Answer 4

s almost a 200:1 ratio for incidence in Australia compared to that in China

Melanoma is often related to UV light (sun exposure is increased in Australia). Additionally, in Australia, genetics play a role because UV light is more damaging in people with fair skin

A large proportion of deaths in Australia are attributable to melanoma

Question 5

Describe the geographical variation of prostate cancer

Answer 5

75:1 ratio for incidence in North America compared to that in China. The incidence is increasing in China, so this ratio will reduce over time

Prostate cancer is detected by looking at PSA levels. PSA is measured in a large proportion of men over the age of 55 in HIGH-INCOME COUNTRIES

The measurement of PSA is suggested to many elderly men in the Western world, because it is a powerful way of detecting prostate cancer early -> Prostate cancer is more likely to be detected in North America (perhaps many silent cases in China).

• there may be a genetic component.

Question 6

Describe the geographical variation of lung cancer

Answer 6

the ratio between Eastern Europe and Western Africa is still relatively high. The vast majority (85-90%) of lung cancers are due to TOBACCO SMOKE. Smoking is extremely frequent in Eastern Europe and Russia. However, smoking prevalence is increasing in Africa with the expansion of tobacco companies

Question 7

What do migrant studies show?

Answer 7

FOLLOWING MIGRATION:

• A rapid change in risk implies that lifestyle/environment factors act late in carcinogenesis
• A slow change in risk suggests that exposures early in life are the most relevant
• Persistence of rates between generations suggests genetic susceptibility is important in determining risk
• The Japanese migrated to the USA. The Japanese that remained in Japan have a VERY HIGH INCIDENCE of stomach cancer. The incidence of stomach cancer in white Americans is very low.
• The Japanese that migrated developed a much lower incidence rate – more similar to that seen in Americans. This was seen in the first generation, and even more so in the second generation.
• The OPPOSITE happened with colon cancer. Colon cancer is rare in Japan and common in the USA. Japanese migrants developed a greater risk of developing colon cancer. This suggests that cancer is heavily influenced by environmental causes.
• In STOMACH and COLON cancer, it is likely that diet is involved, but ALSO infections (e.g. H. pylori). Cancer is a ‘genetic’ disease, in the sense that it is related to changes in DNA. HOWEVER, cancer is essentially not an inherited disease. There are a small proportion (5-10%) of ‘inheritable’ cancers, in which mutations that pre-dispose individuals to cancer are passed on. Other mutations may be introduced by mutagens

Question 8

What are the main risk factors for cancer?

Answer 8

SMOKING: Smoking accounts for at least 30% of all cancer deaths (90% in men, 80% in women). Smoking is associated with increased risk for at least 15 types of cancers

DIET: We still don’t entirely know how diet plays into cancer aetiology. However, fibres DO protect us from colon cancers – increasing fibre intake decreases colon cancer risk

ALCOHOL: All types of alcohol are responsible for oral, pharynx, larynx, and oesophagus and liver cancers. The mechanisms are poorly understood, but there’s synergism with tobacco. Balance with preventive effect for CHD

ANTHROPOMETRY: Increased BMI and obesity are associated with types of cancer (breast, prostate and endometrium). Particularly post-menopausal breast cancer

*Western Lifestyle: Energy dense diet, rich in fat, refined carbohydrates and animal protein. Low physical activity. Smoking and drinking

Question 9

What percentage of cancers are caused by infectious agents?

Answer 9

16% of cancer cases are likely to be caused by infectious agents worldwide:

• 25% in Africa
• <10% in Europe (1 in 33 in UK)