Depression and cancer commonly co-occur. The prevalence of depression among cancer
patients increases with disease severity and symptoms such as pain and fatigue. The
literature on depression as a predictor of cancer incidence is mixed, although chronic
and severe depression may be associated with elevated cancer risk. There is divided
but stronger evidence that depression predicts cancer progression and mortality, although
disentangling the deleterious effects of disease progression on mood complicates this
research, as does the fact that some symptoms of cancer and its treatment mimic depression.
There is evidence that providing psychosocial support reduces depression, anxiety,
and pain, and may increase survival time with cancer, although studies in this latter
area are also divided. Psychophysiological mechanisms linking depression and cancer
progression include dysregulation of the hypothalamic-pituitary-adrenal axis, especially
diurnal variation in cortisol and melatonin. Depression also affects components of
immune function that may affect cancer surveillance. Thus, there is evidence of a
bidirectional relationship between cancer and depression, offering new opportunities
for therapeutic intervention.