What, if any, is the relationship between stress and cancer?

There is a widespread belief that stress can lead to susceptibility to cancer. However, at the present time, the evidence for this belief is mixed. In a meta-analysis of 29 studies, Petticrew, Fraser, and Regan concluded that whereas analysis of their larger study's sample found that adverse life events were twice as likely to be reported by breast cancer patients than by controls, when poorer quality studies were eliminated from their analysis, there did not appear to be a causal relationship between these variables. Current research findings continue to confirm that at most there is only a weak association between life stress and losses in adulthood and breast cancer risk.

Researchers have also discovered a positive relationship between stressful events such as foot-shock and subsequent tumor growth in animals such as mice. However, as discussed by Levinson and Bemis, it is difficult to generalize from mice to humans regarding this issue for several reasons. These rodent strains have been specifically bred to develop cancers from viruses, a process that is uncommon in humans, occurring in only 2 to 3 of known human cancers. In addition, when these animals are exposed to carcinogens, it is typically at very high doses, which does not match the chronic low-dose exposure that humans with cancer may have had in the real life environment.