Immune reaction links disease progression in cancer patients with depression.

Mood disturbances and depression are supposed to have a negative impact on patients' outcome in malignant tumour disease. On the other hand, poor prognosis in cancer patients is associated with chronic immune challenge which is paralleled by enhanced degradation of the essential amino acid tryptophan and thus decreased plasma tryptophan concentrations. Because tryptophan is precursor for the biosynthesis of the neurotransmitter serotonin (= 5-hydroxytryptamine, 5HT), low tryptophan concentrations will lead to decreased availability of serotonin which finally increases the susceptibility for the development of mood disturbances and depression in the patients. Thus, the development of depression in cancer patients may result from chronic cellular immune stimulation. In conclusion, a more aggressive tumour rather than depression will be responsible for worse outcome of cancer patients and will be associated with a more drastic challenge of the immune system, as a side effect leading to neurotransmitter disturbances.