Depression and anxiety are the core disorders causing emotional distress in patients (pts) with metastatic breast cancer. The aim of our study was to screen metastatic breast cancer outpatients for anxiety and depression, and to investigate the influence of age, Karnofsky Performance Status (KPS), cancer activity, and inflammation as represented by IL-6 levels on these two mood disorders. Pts treated with chemotherapy for metastatic breast cancer (n = 70) were assessed using the Hospital Anxiety and Depression Scale (HADS) for symptoms (scores 0-21) and caseness (score ≥11) of clinical depression and anxiety. Blood samples for IL-6 concentrations were collected at 10:00 a.m. A total of 22 (31.4 %) pts were diagnosed with caseness of clinical depression and 23 (32.9 %) pts with clinical anxiety, while 12 pts were diagnosed positive for both mood disorders. Depression and anxiety were positively but moderately correlated (Spearman's r (2) = 0.24, p < 0.001). IL-6 was significantly correlated with symptoms of depression (r (2) = 0.42, p < 0.001) and to a lesser extent to symptoms of anxiety (r (2) = 0.16, p = 0.001). In addition, IL-6 was positively associated with tumor progression (p < 0.001). Multiple linear regression analysis showed that tumor progression (standardized b = 0.226, p = 0.047), symptoms of anxiety (b = 0.292, p = 0.016), and IL-6 (b = 0.314, p = 0.007) were independently associated with clinical depression, whereas anxiety was linked to tumor progression (b = 0.238, p = 0.030), symptoms of depression (b = 0.407, p < 0.001) and age (b = -0.381, p < 0.001), but not to IL-6 (b = 0.168, p = 0.134). Even though a positive correlation between depression and anxiety exists, clinical parameters like age, cancer activity, KPS, and IL-6 do influence depression and anxiety differently. Unlike clinical depression, anxiety is not associated with increased IL-6 levels, however, shows a reciprocal correlation with age.