Soluble CD206 in metastatic renal cell carcinoma: Relation to clinical-biochemical parameters and patient outcome

The mannose receptor (MR/CD206) is a marker of M2-like tumor-associated macrophages. Membrane CD206 can be shed, releasing the receptor as a soluble protein (sCD206), which can be measured in serum. Here, we investigated the biomarker potential of sCD206 in patients with metastatic renal cell carcinoma (mRCC). Serum sCD206 was measured by an enzyme-linked immunosorbent assay in 88 mRCC patients and 20 healthy controls (HCs). At diagnosis, serum sCD206 was elevated in patients with intermediate-risk mRCC according to the Memorial Sloan Kettering Cancer Center (MSKCC) risk score, compared to both HCs and patients with favorable MSKCC risk score. Furthermore, sCD206 levels correlated with both sCD163 and C-reactive protein. Soluble CD206 levels decreased after treatment initiation (p < .0001 at 5 weeks) but with a tendency toward elevated levels at time of progression, compared to baseline (p = .06). In univariate survival analysis, high levels of serum sCD206 at baseline was a significant risk factor associated with reduced overall survival (hazard ratio [HR] = 1.37, 95% confidence interval: 1.12-1.67, p = .002). Stratified by clinical risk scores, increased sCD206 was still a statistically significant risk factor of overall mortality (p < .01) in the intermediate-risk group by both the MSKCC (HR = 1.48) and the newer International Metastatic RCC Database Consortium (IMDC) score (HR = 1.53). Furthermore, addition of sCD206 as a dichotomized variable to the IMDC risk score enabled separation of the intermediate-risk group into two groups with survival comparable to those with favorable and poor risk, respectively. Overall, sCD206 is a potential add-on biomarker for mRCC patients in the intermediate-risk group of the current clinical risk scores.