Monocyte/macrophage-derived soluble CD163: a novel biomarker in multiple myeloma.

Macrophages play an important role in cancer by suppression of adaptive immunity and promotion of angiogenesis and metastasis. Tumor-associated macrophages strongly express the hemoglobin scavenger receptor CD163, which can also be found as a soluble protein in serum and other body fluids (soluble CD163, sCD163). In this study, we examined serum sCD163 as a biomarker in patients with newly diagnosed multiple myeloma. Peripheral blood (n = 104) and bone marrow (n = 17) levels of sCD163 were measured using an enzyme-linked immunosorbent assay. At diagnosis, high sCD163 was associated with higher stage according to the International Staging System (ISS) and with other known prognostic factors in multiple myeloma (creatinine, C-reactive protein, and beta-2 microglobulin). Soluble CD163 decreased upon high-dose treatment, and in a multivariate survival analysis including the covariates treatment modality and age at diagnosis, higher levels of sCD163 were associated with poor outcome (HR = 1.82; P = 0.010). The prognostic significance of sCD163 was lost when including ISS stage in the model (HR = 1.51; P = 0.085). Soluble CD163 values were significantly higher in bone marrow samples than in the matched blood samples, which indicate a localized production of sCD163 within the bone marrow microenvironment. Soluble CD163 was found to be a prognostic marker in patients with multiple myeloma. This may indicate that macrophages and/or monocytes have an important role in the bone marrow microenvironment of myeloma patients, supporting myeloma cell proliferation and survival. We propose the serum sCD163 value 1.8 mg/L as a cutoff concentration for survival analysis in patients with multiple myeloma, which should be validated in future studies.