Comparison of serum levels of syndecan-1 (SYN) in different phases of multiple myeloma and in monoclonal gammopathy of undetermined significance. Vertical axis: serum levels of syndecan-1 (SYN, ng/mL). Horizontal axis: (A) multiple myeloma at the time of diagnosis, (B) multiple myeloma (MM) in relapse/progression, (C) remission phase multiple myeloma, (D) monoclonal gammopathy of undetermined significance (MGUS). The differences between active phase MM (A versus B), and remission phase myeloma and MGUS (C and D) were not statistically different. Significant differences were found between MM at the time of diagnosis and remission phase myeloma (A versus C; M 103,25 versus 31,06 ng/mL, P < 0,0001), MM at the time of diagnosis and MGUS (A versus D; M 103,25 versus 28,0 ng/mL, P < 0,0001), MM in relapse/progression and remission phase MM (B versus C; M 58,0 versus 31,06 ng/mL, P < 0,0001), and MM in relapse/progression and MGUS (B versus D; M 58,0 versus 28,0 ng/mL, P < 0,0001).