Role of endothelial cells and fibroblasts in multiple myeloma angiogenic switch

Multiple myeloma (MM) mainly progresses in bone marrow (BM). Therefore, signals from the BM microenvironment are thought to play a critical role in maintaining plasma cell growth, migration, and survival. Reciprocal positive and negative interactions between plasma cells and microenvironmental cells, including endothelial cells (ECs) and fibroblasts may occur. The BM neovascularization is a constant hallmark of MM, and goes hand in hand with progression to leukemic phase. Microenvironmental factors induce MMECs and fibroblasts to become functionally different from monoclonal gammopathy of undetermined significance (MGUS) ECs (MGECs), i.e., to acquire an overangiogenic phenotype, and be similar to transformed cells. These alterations play an important role in MM progression and may represent new molecular markers for prognostic stratification of patients and prediction of response to antiangiogenic drugs, as well as new potential therapeutic targets.