Mind-body effect: Insulinlike growth factor-1; clinical depression; and breast, prostate, and other cancer risk - An unmeasured and masked mediator of potential significance?

A possible relation may exist between higher insulinlike growth factor (IGF)-1 levels and the risk of premenopausal breast, prostate, or other cancers from recent prospective and case-control studies. Separately, a large prospective study has shown a potential association between chronic depression and cancer risk, whereas other preliminary studies have suggested a link between increasing IGF levels with major depression. Other studies have found that certain standard cancer treatments reduce the effect and levels of IGF, and 1 small study has found that standard antidepressants may reduce IGF levels in some patients diagnosed with major depression. It is possible that IGF-1 (or other IGFs) may be a mediator between depression and cancer, because separately both have been implicated in the risk of various cancers. This hypothesis first and foremost relies on the unsettled notion that an actual relation already exists or may be found in the future. It requires more extensive investigation because several studies have not found an association between IGF or depression and cancer risk, and other limitations such as small sample sizes and other influential factors on IGF levels need to be elucidated. Whether or not a mind-body effect exists with cancer, as seems to be the case with other diseases, remains to be seen. Is depression a potential confounder of human studies that attempts to establish a relation between IGF and disease? All of the studies to date have attempted to at least determine the effect of a variety of factors on IGF levels - including age, sex, diet, family history, weight, smoking status - and then have adjusted their results accordingly. Depression has not been included in this list of potential factors that may need to be considered when analyzing IGF-1 data and cancer risks. The time seems ripe to at least define further the relation, if any, between IGF-1 and depression.