Studies show that the incidence in women who migrate from low to high-risk regions, slowly rises, over two or three generations, to the rates of the host country. This illustrates the importance of lifestyle as well as hormonal risk factors in the development of the disease. Other risk factors are obesity after menopause, and diet, in particular too high a consumption of animal fats. At least half of breast cancer sufferers survive at least five years after diagnosis. Three out of four cases worldwide are in developing countries.
Studies indicate a protective effect of a diet rich in vegetables and fruit.
Eighty per cent of cases occur in developing countries, where it is often the most common cancer in women. Cases and deaths have declined markedly in many industrialized countries, mainly because of extensive screening programmes. A vaccine against the virus is being developed. Once, these diseases were regarded as affecting exclusively industrialized nations, but this is no longer true. As developing countries modernize, they are more able to control communicable diseases, and the life expectancy of their populations increases.