Social inequalities and cancer.

Why study socioeconomic factors and cancers? Inequalities in health reflect social inequalities in society; they provide perhaps the most convincing index of inequality (Chapter 2). Despite attempts to change the social structure and to arrive at a more egalitarian society, social inequalities have not disappeared and seem even to be increasing worldwide. At the global level, socioeconomic differences in health are stark. They are apparent in the worse sanitary conditions, higher mortality, lower life expectancy and lower cancer survival rates of the populations of developing countries compared with those of industrialized countries. Differences in cancer risk are also seen within industrialized countries between the socioeconomically less and more favoured population groups. In certain areas of industrialized countries, social and environmental conditions comparable with those existing in the poorest countries of the world have been recreated. However, social inequalities in health are not limited to those of lowest socioeconomic status but operate across the whole of society. The occurrence of cancer within a population can be studied at many different levels, including forms of social entities, 'the individual', a particular organ system, or a particular molecule (Chapter 1). The causes of cancer can also be studied at these different levels, including socioeconomic factors, lifestyle, and genetic alterations in a clone of cells. Clearly, there are advantages in understanding disease causation at all of the different levels at which it can be analysed. Although cancer risk factors such as tobacco smoke may appear to operate mainly at the individual level, exposure may occur due to a wide range of political, economic and social factors; conversely, tobacco smoke ultimately has effects at the cellular and molecular levels, including the production of mutations in crucial genes. Of course, it is important to gain information, and take action, at all possible levels, but the history of public health shows that changes at the population level are usually more fundamental and effective than changes at the individual level, even when a single risk factor accounts for most cases of disease. In this sense, a risk factor such as smoking can be regarded as a secondary symptom of deeper underlying features of the social and economic structure of society. Thus, just as a variety of health effects in various organ systems (for example, various types of cancer) may have a common contributing cause (for example, tobacco smoking) at the level of the individual, a variety of individual exposures (for example, smoking and diet) may have common socioeconomic causes at the population level.