Asymptomatic pre-malignant disorder associated with relatively low risk (on average 0.5%-1.0% per year) of progression to multiple myeloma or related plasma cell proliferative malignancies.
No aetiological risk factors have been defined. Male gender, older age, family history of monoclonal gammopathy of undetermined significance, black ancestry, and exposure to radiation or pesticide are associated with a higher prevalence.
There is no indication for specific treatment. Clinical- and laboratory-based follow-up is recommended.
Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic disorder associated with an increased risk of developing multiple myeloma and related plasma cell proliferative malignancies. The following criteria must be met for diagnosis: 1) presence of a monoclonal (M) protein in the serum (at a concentration <30 g/L [3 g/dL]) or in urine (<500 mg per 24 hours); 2) <10% plasma cells in the bone marrow (a bone marrow examination is only required if M protein is >15 g/L [1.5 g/dL], or for non-IgG MGUS, or if the free light chain ratio is abnormal); and 3) an absence of lytic bone lesions, anaemia, hypercalcaemia, renal insufficiency, or amyloidosis related to the plasma cell proliferative process. 
Professor of Medicine
Division of Hematology
SK has served as a consultant for Janssen, Abbvie, Amgen, Merck, Celgene, Takeda, and Skyline.
Professor Shaji Kumar would like to gratefully acknowledge Dr Ola Landgren, a previous contributor to this topic. OL is an author of several references cited in this monograph.
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