Between the body and the mind: the involvement of psychological factors in the development of multifactorial diseases.

A possible aetiological role for psychological factors has been propounded in particular in relation to diseases of which the causes are only partially known and which are in most cases multifactorial, such as cancer. The long period between a possible first event and the point of no return, gives appeal to the belief that life events other than "material" causes may play a role in cancer. The evidence that the immune and the nervous system may produce the same substances has opened the way to a new area of research. However, a lack of standardised instruments and the difficulty of conducting systematic and adequate analyses of potential confounding variables have discouraged most qualified scientists from devoting time and effort to investigating the possible role of psychological factors in the aetiology of human diseases. A few studies have reported a positive association between severe life events and breast cancer, but the prevailing view of the medical establishment is that there is no true association between stress and the onset of breast cancer. Although many criticisms of the studies reporting a positive association are definitely based on solid arguments, at least some of the criticisms cling to the requirement for absolute certainty in establishing a cause-effect relationship, which epidemiological studies can rarely, if ever, provide. A challenge for the future of research will be to investigate and better understand the role of subjective factors on the course and outcome of various pathologies, and in modulating the risk of developing a pathology.