Prognostic role of interleukin-6 in renal cell carcinoma: a meta-analysis

Background To evaluate the prognostic role of interleukin-6 (IL-6) in renal cell carcinoma (RCC). Method Relevant research articles were obtained from literature databases. Data were extracted from study reports which reported IL-6 levels in relevance to RCC prognosis and random-effects meta-analyses were performed to estimate IL-6 levels, percentage of patients with high IL-6 levels, and hazard/odds ratios between high and low IL-6 levels in survival outcomes. Results 22 studies (1976 patients; age 59.9 years [95% confidence interval (CI) 58.0, 61.8]; 33% [95% CI 29, 36] females) were included. IL-6 levels in RCC patients ranged from 8.9 +/- 13-193 +/- 101 picograms per milliliter (pg/ml) which were higher than those of normal healthy individuals (mean difference 13.96 pg/ml [95% CI: 1.52, 26.40]; p = 0.03). Percentage of RCC patients with high IL-6 levels was 48.98% [95% CI 42.94, 55.03] and this rate was greater in advanced (51.73% [95% CI 45.94, 57.53]) than in local (40.75% [95% CI 26.23, 55.27]) RCC. Survival was longer in patients with low compared to high IL-6 levels (MD 9.65 months [95% CI 5.01, 14.29]; p < 0.0006 and hazard ratio 3.03 [95% CI 2.37, 3.70]). Treatment response rate was significantly higher in patients with low IL-6 than high IL-6 levels (odds ratio 5.11 [95% CI 2.21, 11.77]; p < 0.00001). There was a strong correlation between IL-6 and c-reactive protein levels (correlation coefficient 0.622 [95% CI 0.431, 0.760]; p = 0.00001). Conclusion IL-6 levels are much variable in RCC patients. High levels of IL-6 in RCC patients are associated with poor survival.