Effect of Wnt3A in the bone microenvironment in multiple myeloma. (A) Myeloma cells promote the development of the associated bone disease, and the bone disease promotes tumor growth and survival, resulting in a vicious cycle of increased tumor burden and increased osteolytic bone disease. (B) Wnt3A enhances Wnt signaling in the bone marrow microenvironment. This has no direct effect on myeloma-cell growth, but acts to increase bone formation and decrease bone resorption. This inhibits myeloma bone disease and, consequently, indirectly reduces tumor burden in bone. Professional illustration by Alice Chen.