Myeloma cells reside in specialised microenvironments, which is called myeloma niche. Myeloma niche provides important cell-cell interactions and signalling molecules that regulate localization and proliferation of myeloma cells. stromal cell-derived factor 1(SDF-1)/Chemokine (C-X-C Motif) Receptor 4 (CXCR4) plays an important role in this process. G-CSF is reported to induce stem cell mobilization by decreasing bone marrow SDF-1. Our in vitro study found that G-CSF enhanced bortezomib activity by inhibiting SDF-1/CXCR4. Myeloma patients treated with Bortezomib, Cyclophosphamide and Dexamethasone have achieved a relatively good response, with an ORR about 80% and complete remission about 40%. We hypothesized that G-CSF may mobilize myeloma cells from myeloma niches thus to enhance bortezomib activity.