Cancer epidemiology is the study of the incidence of cancer as a way to infer possible trends and causes. A founding paper of this discipline was the work of Richard Doll and A. Bradford Hill, “Lung Cancer and Other Causes of Death In Relation to Smoking. A Second Report on the Mortality of British Doctors,” (British Medical Journal 1956). Richard Droll left the London Medical Research Center (MRC), to start the Oxford unit for Cancer epidemiology in 1968. With the use of computers, the unit was the first to compile large amounts of cancer data. Modern epidemiological methods are closely linked to current concepts of disease and public health policy. Over the past 50 years, great efforts have been spent on gathering data across medical practise, hospital, provincial, state, and even country boundaries, as a way to study the interdependence of environmental and cultural factors on cancer incidence.

The biggest problem facing cancer epidemiology today is the changing concept of ‘cancer incidence’. For example, a breast cancer tumor with a very slow growth rate may be found with a mammogram at 50 years, while the same tumor may have been found as a noteworthy ‘lump’ at 70 years, depending on the specific growth factors affecting that particular patient’s case. As diagnostic tools improve, this has a direct impact on the epidemiological data.

In some Western countries, such as the USA and the UK, cancer is overtaking cardiovascular disease as the leading cause of death. In many Third World countries cancer incidence (insofar as this can be measured) appears much lower, most likely because of the higher death rates due to infectious disease or injury. With the increased control over malaria and tuberculosis in some Third World countries, incidence of cancer is expected to rise; this is termed the epidemiologic transition in epidemiological terminology.

Cancer epidemiology closely mirrors risk factor spread in various countries. Hepatocellular carcinoma (liver cancer) is rare in the West but is the main cancer in China and neighboring countries, most likely due to the endemic presence of hepatitis B and aflatoxin in that population. Similarly, with tobacco smoking becoming more common in various Third World countries, lung cancer incidence has increased in a parallel fashion.