Routine screening for monoclonal gammopathy of undetermined significance (MGUS) is not indicated. Despite this fact, MGUS is a common finding in medical practice. Almost all individuals diagnosed with MGUS represent incidental cases diagnosed when physicians order serum protein electrophoresis, immunofixation, or both, as part of the work-up of a number of common symptoms and laboratory abnormalities. In the absence of reliable molecular predictors of outcome, the detection of an early precursor state typically imposes a complex situation for the patient and the responsible physician-usually, it leads to a lot of questions that lack clear answers. In the past years, several novel insights have been gained in the area of multiple myeloma (MM) precursor disease. This review focuses on results from recent investigations and discusses implications for diagnostic work-up, clinical management, and patient counseling. More specifically, it sheds light on the following commonly asked questions by patients and physicians: i) what is the risk of progression from precursor to full-blown MM, and are there ways to risk-stratify patients?; ii) is MM always preceded by a precursor state, and is there anything that could or should be done to delay or prevent progression?; and iii) why do some individuals develop MM precursor diseases, and is there a reason to screen the family?
Definitions and Epidemiology
From 'Benign Monoclonal Protein' to Monoclonal Gammopathy of Undetermined SignificanceThe concept of monoclonal versus polyclonal gammopathies was initially raised in 1960 by Jan Waldenström, 1 who described patients with a narrow band of hypergammaglobulinemia on electrophoresis as having a monoclonal-or M-protein. Many of these patients had multiple myeloma (MM) or macroglobulinemia, while others had no evidence of malignancy. Waldenström considered these patients to have "essential hypergammaglobulinemia" or a "benign monoclonal protein."Based on the observation that otherwise healthy individuals with these protein abnormalities turned out to have an excess risk of developing MM, Waldenströ m's macroglobulinemia, light-chain amyloidosis, or related disorders, Robert Kyle coined the term "monoclonal gammopathy of undetermined significance" (MGUS) in 1978. 2 According to diagnostic criteria provided by the International Myeloma Working Group (IMWG) in 2010, 3 MGUS is defined as follows (and all three criteria must be met): i) serum monoclonal protein under 3 g/dL; ii) clonal bone marrow plasma cells under 10%; and iii) absence of end-organ damage such as hypercalcemia, renal insufficiency, anemia, and bone lesions that can be attributed to the plasma-cellproliferative disorder.Screening studies have found MGUS to be present in approximately 3.2% of Caucasians above the age of 50 years. 4 Prevalence appears to be roughly twice as high among African men, African-American women, and obese individuals. 5,6 Chronic antigen stimulation 7-11 and pesticide exposure have also been associated with an excess risk of MGUS/MM. 12,13 Rece...