Biomarkers of depression in cancer patients

Inflammation and perturbation of the hypothalamic-pituitary-adrenal (HPA) axis function appears to play a putative role in the etiology of depression. Patients with metastatic cancer demonstrate elevated prevalence rates for depression. The objective of the current study was to illustrate the efficacy of interleukin-6 (IL-6) and HPA axis function as adjuncts to support the diagnosis of depression in cancer patients.

Plasma concentrations of IL-6 and cortisol were measured in 114 cancer patients with and without depression. The relative diurnal variation of cortisol (cortisol VAR), expressed as a percentage, was calculated. Receiver operating characteristics analysis was performed.

Depression was associated with increased plasma concentrations of IL-6 (18.7 pg/mL vs. 2.7 pg/mL; P < .001) and higher cortisol concentrations at 8 AM and 8 PM. The relative cortisol VAR (11.7% vs. 60.6%, respectively; P < .001) was found to be decreased in cancer patients with depression, indicating a disturbed circadian function of the HPA axis. As a biomarker of depression, IL-6 yielded at a cutoff value of 10.6 pg/mL, a sensitivity of 79%, and a specificity of 87% (area under the curve [AUC] = 0.86; 95% confidence interval [95% CI], 0.78-0.94), whereas cortisol VAR demonstrated a sensitivity of 81% and a specificity of 88% (AUC = 0.85; 95% CI, 0.74-0.97) at a cutoff value of 33.5%.

Depression is associated with increased plasma IL-6 concentrations in patients with cancer. These patients demonstrate a dysfunction of the HPA-axis, characterized by a decreased diurnal variation of cortisol. The high sensitivity and specificity of these parameters biomarkers of depression make IL-6 and cortisol VAR helpful tools in the diagnosis of depression in patients with cancer.