Higher Than Normal Plasma Interleukin-6 Concentrations in Cancer Patients With Depression: Preliminary Findings

Objective: This study investigated whether cancer patients with and without major depression exhibit immune system abnormalities similar to those reported in medically healthy, depressed subjects without cancer. Method: The study subjects consisted of patients diagnosed with pancreatic, esophageal, or breast cancer. Other groups consisted of subjects with major depression (without cancer) and healthy comparison subjects. Subjects’ diagnoses were made with the Structured Clinical Interview for DSM-III-R. Severity of depression was measured with the Hamilton Depression Rating Scale. Plasma concentrations of interleukin-6 (IL-6) and postdexamethasone cortisol were measured. Results: Cancer patients with depression had markedly higher plasma concentrations of IL-6 than healthy comparison subjects and cancer patients without depression. Although significant correlations were found between Hamilton depression scale scores and plasma concentrations of postdexamethasone cortisol, no significant correlations were found between plasma IL-6 and postdexamethasone cortisol concentrations. Conclusions: Higher than normal plasma IL-6 concentrations were associated with a diagnosis of major depression in cancer patients. IL-6 may contribute to sickness behavior that has overlapping symptoms with major depression. (Am J Psychiatry 2001; 158:1252–1257) Cancer patients, who experience marked physiologic, economic, and psychological stressors, have long been observed to have elevated prevalence rates of major depression, compared with the general population (1). Among cancer patients, the highest prevalence rates are exhibited by patients with either oropharyngeal cancer (2–4) or pancreatic cancer (5–7). Prospective or crosssectional studies of patients with pancreatic cancer have documented a remarkable point prevalence rate of depression of 50% (5–8). Although a number of neurochemical, neuroendocrine, neuroanatomical, and neuroimmune alterations have been associated with unipolar depression, few of these psychobiologic alterations have been systematically investigated in cancer patients with depression.