Dickkopf-1 (Dkk-1) and sclerostin are inhibitors of the Wingless-type and integrase 1 (Wnt) signaling and they are implicated in the pathogenesis of multiple myeloma (MM) bone disease through inhibition of osteoblast function. There is very limited information for the circulating levels of Dkk-1 and sclerostin in different phases of MM and their alterations post therapies with novel agents. Therefore, we studied 284 MM patients (153M/131F, median age 66 years): 167 consecutive patients were newly-diagnosed (20 had asymptomatic MM and 147 symptomatic MM), 29 patients were at the plateau phase of MM and 88 patients had relapsed/refractory MM and received therapy with the combination of lenalidomide plus dexamethasone with or without bortezomib (VRD or RD; Dimopoulos et al, Leukemia 2010). For newly diagnosed patients, serum was stored at the time of diagnosis, while for patients at the plateau phase serum was collected at the time of confirmation of the plateau (at least 6 months with stable M-protein without criteria confirming progression) and for relapsed/refractory patients on day 1 of cycles 1, 4 and 7 of VRD or RD administration. Circulating levels of Dkk-1 and sclerostin were measured using ELISA methodology (R&D Systems, Minneapolis, MN, USA and Biomedica Medizinprodukte, Vienna, Austria, respectively) in all patients and in 20 gender- and age- matched healthy controls. Circulating Dkk-1 and sclerostin concentrations of newly diagnosed symptomatic patients (median: 1383 pg/mL, range:274-32, 862 pg/mL and 415 pg/mL, 0–3,340 pg/mL respectively) were increased compared to controls (1069 pg/mL, 540-2, 709 pg/mL; p<0.001 and 250 pg/mL, 0–720 pg/mL; p=0.03, respectively) and to asymptomatic patients at diagnosis (1044 pg/mL, 480-2, 335 pg/mL; p<0.001 and 140 pg/mL, 0–1,100 pg/mL; p=0.001, respectively). Patients at plateau phase had increased circulating levels of sclerostin (704 pg/mL, 68–2000 pg/mL; p <0.001) compared to controls (p=0.002) as well as to MM patients at diagnosis (p=0.02). In contrast, they had lower serum levels of Dkk-1 (1013 pg/mL, 414–1729 pg/mL) compared to MM patients at diagnosis (p<0.001) and no difference compared to controls. Patients with ISS-3 myeloma at diagnosis had higher values of Dkk-1 and sclerostin than ISS-1 and ISS-2 patients [median Dkk-1 values for ISS-1, ISS-2 and ISS-3 were: 1059 pg/mL, 1290 pg/mL and 2649 pg/mL, respectively; p(ANOVA)=0.031; median sclerostin values for ISS-1, ISS-2 and ISS-3 were: 394 pg/mL, 392 pg/mL and 714 pg/mL, respectively; p(ANOVA)=0.001]. Patients with lytic disease at diagnosis (n=116) had increased levels of Dkk-1 compared with patients with no lytic disease (n=51): 1475 pg/mL, 327-32, 862 pg/mL vs. 840 pg/mL, 274–1112 pg/mL; p=0.002. There was no difference in sclerostin levels between these patients; however, patients with advanced bone disease (>3 lytic lesions and/or a fracture) had a borderline increase in their circulating sclerostin compared to all others (p=0.072). Dkk-1 circulating levels correlated weakly with sclerostin (r=0.201, p=0.05). Relapsed patients had increased Dkk-1 (1218 pg/mL, 161-19, 325 pg/mL) and sclerostin (886 pg/mL, 90-6, 272 pg/mL) levels compared to controls and to asymptomatic patients at diagnosis (p<0.001 for all comparisons). In patients who received RD, Dkk-1 was increased and sclerostin was decreased after 6 cycles of therapy. Responders to RD had a median increase of 9% in Dkk-1 serum levels after 6 cycles of therapy, while non-responders had a median increase of 91% compared to baseline values (p<0.01). Patients who did not respond to RD showed an increase in bone resorption marker CTX (p=0.021) after 6 cycles of therapy. VRD administration resulted in a significant reduction of sRANKL (p=0.024) and increase of bone formation marker, osteocalcin (p=0.01) after 6 cycles, but showed only minimal reduction of Dkk-1 (p=0.08) and no alterations on sclerostin. In conclusion our study suggests that Dkk-1 is elevated in active myeloma, while sclerostin is elevated even in the plateau phase of the disease. Both correlated with adverse disease features. The increase of Dkk-1 by RD seems to be balanced by a reduction effect of bortezomib on Dkk-1 in VRD. Furthermore, the reduction of sclerostin in RD patients may represent a modulatory effect of lenalidomide on marrow microenvironment. These results further support the rationale for the use of drugs targeting Dkk-1 and sclerostin in MM.