Breast cancer and the environment

The most recent estimate of the overall worldwide burden of cancer is that in the year 2000 more than 10 million new cancer cases occurred and approximately 6 million cancer deaths. Breast cancer accounts for about 1 in 10 cancers and is the most frequent cancer affecting women. Since 10% of all cancers in the world are breast cancer (only affecting half of the population as breast cancer almost exclusively concerns only women), it is being considered an epidemic. In terms of the absolute number of incident cases, breast cancer now ranks first not only in the industrialized world but also in the developing world. The worldwide mortality figure for the year 2000 was 370,000. However, there are marked geographical differences, with Africa and Asia currently having incidence rates some 10 times lower than those of North America and northern Europe. Studies of migrant populations have long indicated that the genetic background only plays a tiny, if any, role in these differences. Over time, clear increases have been seen in the global number of cases: from 572,000 in 1980 to 1,050,000 in 2000. This corresponds not only to a modest increase in incidence rates in countries with a long history of frequent breast cancer but also to marked increases in countries with previously low rates. The reasons for these increases are currently unexplained and a possible hypothesis relates to environmental factors. By contrast, in a number of countries in the western world mortality rates are stable, and, in the USA and the United Kingdom, even decreasing slightly. The aetiology of breast cancer has been the subject of hundreds of studies since the pioneering investigation of Lane Claypon in 1926. Risk factors belong to different domains: reproductive life, hormonal factors, diet, genetics (BRCA1, BRCA2) and exposure to radiation and selected chemicals. Yet, much breast cancer remains unexplained and new aetiological links must be sought such as occupational factors and exposure to pesticides and other endocrine disrupters. A recent international summit on breast cancer and the environment outlined the need for more research to be conducted into the effects of exposure in the vicinity of nuclear power plants or chemical landfill sites and, more generally, into contaminants in food, air, water and soil. This is particularly relevant in some parts of the world such as Africa.