Mind as a risk factor for cancer—some comments

It is striking how often psychological factors are included in conversations about life in general and illness in particular. We ascribe the occurrence of disease to certain personality traits, recent episodes of stress or major life events. In our understanding of illness, we consider that psychology plays a role in all aspects of the risk, contributes to healing and influences the outcome. With better understanding of the causes of infectious diseases and the availability of treatment strategies for many of them, the role of psychological factors has narrowed down to chronic disease. Most chronic conditions do not appear to be associated with infectious agents, and psychological factors became an obvious target in the search for explanations. In the early studies, it was suspected that chronic diseases such as gastric ulcer, cardiovascular disease, diabetes and asthma were completely or partly associated with mind factors. As the factors that play the major role in the causation of these illnesses became clear, however, psychological factors were largely abandoned as targets for preventive action, although, in relation to cardiovascular disease for instance, it was argued that stress in daily life might be one causal factor. Cancer has regularly been reported to be associated with depressive mood, genuine clinical depression, personality traits and exposure to severe stress such as major negative life events [1]. Perhaps the main reason for suspecting that the mind is associated with the risk for cancer is the lack of other hypotheses with regard to the agents responsible. Despite growing knowledge about cancer risk factors, we do not know the causes of about one-third of the incident cases. The idea that the mind causes cancer also arose from individual experiences of the interactions between stress in the broadest sense and physiological reactions, including heart palpitations, extrasystoles, sweating and a general feeling of dysfunctional homeostasis. The somatic system reacts to psychologically stressful exposures, and these well-known, wellcharacterized psychosomatic interactions have been accepted as proof of concept. The prevailing hypothesis is that exposure to mind-associated factors, including major life events, depression and personality traits, impairs the immune function and subsequently predisposes people to the initiation or promotion of cancer. Thus, patients with well-defined disorders of the immune system are at increased risk for non-Hodgkin lymphoma [2]. As mind factors may also influence lifestyle in general, any association observed might, however, be due to tobacco smoking, alcohol drinking, inadequate physical activity or a poor diet [3]. An adverse lifestyle affects the ability to cope of people suffering from depression, experiencing a major negative life event or living with odd personality traits, which can be difficult in a society that does not accept deviations from the norm. Many different types of study have been conducted to investigate whether there is an association between mind and cancer and, if so, whether it is physiological or indirectly causal. This paper addresses some methodological considerations in studies of the mind as a risk factor for cancer, stressing the advantages of registry-based investigations. The paper does not contain a lengthy and detailed discussion of advantages and limitations of other methodological approaches in this area of research. However, this is the focus in the review [1] by Dalton et al.