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Objectives: Lytic bone disease is a hallmark of multiple myeloma (MM) and is caused by osteoclast activation and osteoblast inhibition. Secretion of Dickkopf (DKK)-1 by myeloma cells is a major factor which causes inhibition of osteoblast precursors. So far, there is no study showing a significant difference in serum DKK-1 levels in MM patients with or without lytic bone lesions. Methods: DKK-1 serum levels were quantified in 184 untreated MM patients and 33 monoclonal gammopathy of undetermined significance (MGUS) patients by ELISA, using a monoclonal anti-DKK-1 antibody. Results: Serum DKK-1 was elevated in MM as compared with MGUS (mean 11 963 pg/mL vs. 1993 pg/mL; P 3 lesions: 3114 pg/mL vs. 3559 pg/mL vs. 24 068 pg/mL; P = 0.002). Conclusion: Using a large series of myeloma patients, we could show for the first time a correlation between DKK-1 serum concentration and the amount of lytic bone disease, indicating that DKK-1 is an important factor for the extent of bone disease and supporting the hypothesis of DKK-1 as a therapeutic target in myeloma bone disease.

Lytic bone disease is a hallmark of multiple myeloma (MM) and is caused by osteoclast activation and osteoblast inhibition. Secretion of Dickkopf (DKK)-1 by myeloma cells is a major factor which causes inhibition of osteoblast precursors. So far, there is no study showing a significant difference in serum DKK-1 levels in MM patients with or without lytic bone lesions.DKK-1 serum levels were quantified in 184 untreated MM patients and 33 monoclonal gammopathy of undetermined significance (MGUS) patients by ELISA, using a monoclonal anti-DKK-1 antibody.Serum DKK-1 was elevated in MM as compared with MGUS (mean 11 963 pg/mL vs. 1993 pg/mL; P0.05). Serum DKK-1 levels significantly correlated with myeloma stage according to Durie and Salmon (mean 2223 pg/mL vs. 15 209 pg/mL in stage I and II/III, respectively; P = 0.005). Importantly, myeloma patients without lytic lesions in conventional radiography had significantly lower DKK-1 levels than patients with lytic bone disease (mean 3114 pg/mL vs. 17 915 pg/mL; P = 0.003). Of interest, serum DKK-1 correlated with the number of bone lesions (0 vs. 1-3 vs.3 lesions: 3114 pg/mL vs. 3559 pg/mL vs. 24 068 pg/mL; P = 0.002).Using a large series of myeloma patients, we could show for the first time a correlation between DKK-1 serum concentration and the amount of lytic bone disease, indicating that DKK-1 is an important factor for the extent of bone disease and supporting the hypothesis of DKK-1 as a therapeutic target in myeloma bone disease.