Mayo Clinic
Rochester, MN, USA

Monoclonal gammopathy of undetermined significance (MGUS) is defined by a monoclonal immunoglobulin concentration in serum of 3 g/dL or less, fewer than 10% plasma cells in the bone marrow, and no evidence of end-organ damage (hypercalcemia, renal insufficiency, anemia, or lytic bone lesions) related to the proliferation of the clonal plasma cells.

Smoldering multiple myeloma, first reported in 1980, is an asymptomatic plasma cell proliferative disorder associated with a high risk of progression to symptomatic MM.