Mind and cancer: do psychological factors cause cancer?

We have reviewed the evidence for an association between major life events, depression and personality factors and the risk for cancer. We identified and included only those prospective or retrospective studies in which the psychological variable was collected independently of the outcome. The evidence failed to support the hypothesis that major life events are a risk factor for cancer. The evidence was inconsistent for both depression and personality factors. Chance, bias or confounding may explain this result, as many of the studies had methodological weaknesses. The generally weak associations found, the inconsistency of the results, the unresolved underlying biological mechanism and equivocal findings of dose–response relationships prevent a conclusion that psychological factors are established risk factors. However, certain intriguing findings warrant further studies, which must, however, be well conducted and large and include detailed information on confounders.