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Monoclonal gammopathy of undetermined significance (MGUS) refers to the presence of serum monoclonal protein at a concentration of 3.0 g/dL or lower in patients without other clinical or pathologic evidence of multiple myeloma or related disorders. To determine the natural history of MGUS, from 1960 through 1994 Mayo Clinic researchers identified 1384 MGUS patients and followed them for a median of 15 years; median age at diagnosis was 72.
MGUS progressed in 115 patients (8%) -- most commonly to multiple myeloma (75 patients), lymphoma (19), primary amyloidosis (10), or macroglobulinemia (7). Risk for progression to any one of these disorders was about 1% per year. The most important risk factor for progression was initial concentration of m…