Diagnostic utility of interleukin-6 (IL-6) for primary bile duct cancer and changes in serum IL-6 levels following photodynamic therapy

OBJECTIVES: Difficult diagnoses and a lack of effective therapy complicate biliary tract malignancies. Interleukin-6 (IL-6) is a human bile duct epithelium growth factor correlated with tumor burden. We evaluated the usefulness of serum IL-6 in the diagnosis of primary BDC and measured changes in serum IL-6 levels following photodynamic therapy (PDT). METHODS: We prospectively measured serum IL-6 levels in patients with BDC (N = 26: 14 patients treated with PDT, 12 with biliary drainage alone), hepatocelluar carcinoma (HCC, N = 26), and healthy adults (N = 23). Serum IL-6 levels were measured by an enzyme-linked immunosorbent assay. Patients with clinical conditions known to increase IL-6 levels were excluded. RESULTS: IL-6 was detected in all patients with BDC and HCC, and in 6 of 23 healthy adults. Median and mean levels of IL-6 were higher in patients with BDC than in both other groups (P < 0.001). Using a 25.8 pg/mL cutoff, IL-6 provided a diagnostic sensitivity of 73% and a specificity of 92%; positive and negative predictive values were 83% and 87%, respectively. Serum levels of IL-6 were correlated with tumor burden in BDC patients. One month after treatment of BDC with PDT, the mean IL-6 level decreased significantly from 282.1 +/- 121.8 to 38.2 +/- 9.9 pg/mL (P = 0.008). CONCLUSIONS: Serum IL-6 concentration is a useful addition to the available tests for the differential diagnosis of BDC, and serves as a marker for monitoring the response to treatment of BDC with PDT.