The strongest associations (PCS ≥ 75% and ≥5 studies) were observed for sociodemographic factors (e.g., high social support, being unmarried), inflammatory markers (IL-6, TNF-α, CRP), psychological factors (e.g., history of depression, distress, anxiety), and somatic factors (e.g., fatigue, low functional status, malnutrition). This evidence concerns the gene IL6 and depressive symptom measurement.