Syndecan-1 in multiple myeloma: relationship to conventional prognostic factors

Syndecan-1 (CD138) mediates myeloma cell adhesion, and loss of syndecan-1 from the cell surface may contribute to myeloma cell proliferation and dissemination and influence the prognosis in patients with multiple myeloma (MM). In order to test this hypothesis, we have evaluated syndecan-1 expression on the surface of malignant plasma cells and soluble forms of syndecan-1 in the serum of 25 newly diagnosed MM patients by flow cytometry and immunosorbent assay. Soluble syndecan-1 levels were significantly higher in MM as compared to controls (P<0.001). Cellular and soluble syndecan-1 was significantly inversely correlated (r=-0.89, P<0.001). The soluble syndecan-1 was significantly higher in non- responders to chemotherapy when compared to responders (P<0.01), and in non- survivors as compared to survivors (P<0.001). In contrast, cellular syndecan-1 expression was significantly lower in non- responders when compared to responders (P<0.01), and in non- survivors as compared to survivors (P<0.05). The levels of soluble syndecan-1 increased from stage I through stage II to stage III, whereas cellular syndecan-1 expression were decreased from high levels in stage III down to a low in stage I, with a statistically significant difference (P<0.01, P<0.05, respectively). There was a significant positive correlation between soluble syndecan-1 and plasma cell count (r=0.079, P<0.001), beta2 microglobulin (r=0.85, P<0.001), serum creatinine (r=0.84, P<0.001), C-reactive protein (r=0.082, P<0.001), alkaline phosphatase (r=0.58, P<0.05) and serum calcium (r=0.77, P<0.01) and a negative correlation with hemoglobin level (r=-0.78, P<0.01), platelets count (r=-0.82, P<0.01) and Albumin level (r=-0.64, P<0.01). Cox regression analysis using soluble syndecan-1 at mean-2SD of the controls could correctly classify patient outcome in 84.0%. The addition of beta2 microglobulin to soluble syndecan-1 increased the predictability of the patients' outcome to 96.7%. We conclude that soluble syndecan-1 levels are negatively correlated to the cellular form and that high levels of soluble syndecan-1 and lower expression of cellular syndecan-1 at diagnosis are negative prognostic factors. Assessment of soluble syndecan-1 and beta2 microglobulin at diagnosis is an independent prognostic system for MM.