Monoclonal gammopathies of undetermined significance and smoldering myeloma

Monoclonal gammopathy of undetermined significance (MGUS) is a clonal plasma cell disorder implicated as a precursor of multiple myeloma (MM), while smoldering multiple myeloma (SMM) is a malignant plasma cell disorder without evidence of a myeloma-defining event(s) (MDE). This is a review article of both disorders outlining their current definition and management according to the current standard of care. We focus on the pathogenesis of MM and the role of MGUS and SMM in the development of active MM. MGUS is a benign disorder and, subsequently, is followed by observation. In contrast, for SMM, although the current standard of care is “watch and wait”, this paper will explore the circumstances in which treatment should be considered to prevent MDE.