3. Epidemiology of cancer Flashcards
Recall the incidence and mortality rates of major adult tumours.
We must distinguish between mortality and incidence (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.
There are differences in distribution regarding individual types of cancer. Top = male, bottom = female. Breast cancer is the main type of cancer in women. In men, there are two big killers: prostate cancer and lung cancer.
Differences in distribution suggest that there is something causal in different geographical territories.
Describe the trend in melanoma in countries such as China and Australia.
For melanoma, there is 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.
Describe the incidence of prostate cancer is North America and China.
For prostate cancer, there is a 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. We are NOT SURE whether early detection does protect people from mortality. Prostate cancer is more likely to be detected in North America (perhaps many silent cases in China).
We know nothing about the causes of prostate cancer (unlike melanoma). There may be a genetic component.
Describe lung cancer incidence in Eastern Europe and Western Africa.
In lung cancer, 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.
What is the trend in incidence and mortality of cancer in high income countries?
In high-income countries, we are observing a plateauing of incidence rates. Mortality rates are decreasing in high-income countries (the picture in low-income countries is COMPLETELY DIFFERENT). This same trend, in high-income countries, is seen in BOTH males and females.
Incidence is increasing for common cancer sites in both high-income (now with plateauing and even decreases) and low-income countries (e.g. breast, colorectum, prostate). Mortality is decreasing in most high-income countries (e.g. -23% between 1990 and 2008 in US men), not in low-income countries. Total burden is increasing because of demographic changes (ageing populations, increasing size), and Westernization of lifestyles.
