Depression as a risk factor for cancer: from pathophysiological advances to treatment implications.

Innate immune activation and inflammation have been posited to play a role in the pathophysiology of both depression and neoplastic growth. Cancer patients experience a threefold higher rate of depression than the general population within the first five years of diagnosis. Chronic depression is associated with increased cancer risk and shortened survival. Although the precise cellular and molecular mechanisms of this bidirectional relationship remain unclear, elevated concentrations of circulating plasma proinflammatory cytokines associated with depression may mediate the neuroendocrine, neural, and immune pathways that account for the relationship. Proinflammatory cytokines, in turn, are known to modulate key neurobiological correlates of depression including hypothalamic-pituitary-adrenal (HPA) axis dysregulation, monoamine neurotransmitter metabolism, and limbic system activity. Research is needed to determine whether optimal depression treatment improves cancer survival and to develop antidepressant strategies that target molecular and cellular mechanisms mediating inflammation and the neurobiological pathways influenced by the proinflammatory cytokines.