The Transformation of the Microenvironment: From Observer to Coordinator in Monoclonal Gammopathy of Undetermined Significance (MGUS) to Myeloma Development

Monoclonal gammopathy of undetermined significance (MGUS) is a common asymptomatic plasma cell disorder and the major precursor state of multiple myeloma (MM). Although progression is partly shaped by intrinsic genetic and epigenetic changes within the plasma cell clone, increasing evidence indicates that the bone marrow microenvironment plays a decisive role in determining whether the clone remains clinically silent or evolves toward symptomatic disease. This review examines how the marrow niche changes across the MGUS-SMM-MM continuum. In early MGUS, the microenvironment may already be permissive, but it remains partly restrained: immune control is not fully lost, stromal activation is incomplete, vascular remodeling is limited, and the bone-remodeling compartment has not yet become overtly tumor-supportive. Progression appears to occur when these initially modest stromal, vascular, skeletal, immune, and extracellular matrix alterations become functionally connected. Once linked, these changes form reinforcing circuits that enhance plasma cell retention and survival, weaken immune containment, remodel the vascular and skeletal niche, and promote resistance to therapy. In this view, MGUS-to-MM progression is not simply a plasma cell-autonomous process, but a gradual ecological shift in which the marrow niche becomes increasingly aligned with the needs of the malignant clone. Understanding this coordinated microenvironmental remodeling may improve risk stratification and support therapeutic strategies that target both the plasma cell clone and its supportive niche.

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