ABSTRACT
Cancer has afflicted humans throughout recorded history. The origin of the word ‘cancer’ has been credited to Hippocrates (460-370 bc) who used the terms ‘carcinos’ and ‘carcinoma’ to describe tumours. In Greek these words refer to a crab, most likely because the finger-like spreading projections from a cancer called to mind the shape of a crab. Carcinoma is the most common type of cancer. Cancer is not one disease, but a set of diseases characterized by unregulated cell growth leading to invasion of surrounding tissues and spread to other parts of the body. It is a leading cause of morbidity and mortality, accounting for around
Introduction 165 ❚
Carcinogenesis 167 ❚
Mechanisms 176 ❚
Summary 181 ❚
Study tasks 182 ❚
Notes 182 ❚
Further reading 183 ❚
one-quarter of all deaths in developed countries such as the United States, the United Kingdom, Australia and Canada, where the lifetime risk of developing cancer is around one in three. Moreover, cancer is becoming an increasingly important factor in the global burden of disease – the World Health Organization (WHO) estimates that the number of new cases annually will rise from ten million in 2000 to 15 million by 2020. Plate 7 shows examples of four different kinds of cancer. The role of environmental factors in cancer causation is illustrated by the enormous geographical differences in incidence world-wide. For example, Australia has an incidence of skin cancer that is 155 times higher than that in Japan. These differences cannot be explained fully by genetic factors, as studies of migrants have shown. For example, the incidence of stomach cancer is much higher in Japan than in Hawaii, while the incidence of breast cancer is lower. When Japanese people migrate to Hawaii, their incidence rates for these two cancers move towards the rates in the indigenous population (Figure 8.1). Second-generation migrants experience rates even closer to those of the host country, presumably because they have been exposed for longer than their parents to the environmental factors that prevail in the host country. Contrary to public perception, therefore, some risk factors for cancer can be changed and some cancers prevented. For instance, of the seven million deaths from cancer world-wide in 2001, an estimated 35% have been attributed to nine potentially modifiable risk factors, including physical inactivity (Danaei et al. 2005).
