Table 1.

Definition of MGUS, SMM and symptomatic multiple myeloma.

International Myeloma Working Group criteria, 2010 version [35]
MGUS	Serum M protein < 3 g/dl Clonal bone marrow plasma cells < 10% Absence of myeloma defining events and amyloidosis
SMM	Serum M protein ≥ 3 g/dl and/or clonal bone marrow plasma cells 10 - 60% or urinary monoclonal protein > 500 mg per 24 or FLC ratio < 0.125 or > 8 or ≥ 95% abnormal plasma cells in the bone marrow or immunoparesis of one or more immunoglobulins Absence of myeloma defining events and amyloidosis
MM	Clonal bone marrow plasma cells ≥ 10% and/or biopsy proven plasmacytoma Presence of serum and/or urinary monoclonal protein at any level
CRAB criteria	Evidence of end-organ damage that can be attributed to the underlying plasma cell proliferative disorder (CRAB criteria) Hypercalcemia: serum calcium > 0.25 mmol/l above upper limit of normal or > 2.75 mmol/l (> 1 mg/dl above upper limit of normal) Renal insufficiency: creatinine clearance < 40 ml per min or serum creatinine > 177 μmol/l (> 2 mg/dl) Anemia: normochromic, normocytic with a hemoglobin value of > 2 g/dl below the lower limit of normal or a hemoglobin value < 10 g/dl Bone lesions: lytic lesions, or osteoporosis with compression fractures. If osteoporosis is used as the sole criterion, then the bone marrow has to be > 30% involved
MDE criteria	Or any MDE as follows: Clonal bone marrow plasma cell percentage ≥ 60% [22] An abnormal FLC-ratio ≥ 100 (involved kappa) or < 0.01 (involved lambda) [23] Two or more focal lesions on MRI or positron emission tomography-CT studies measuring > 5 mm in diameter [24,25]

FLC: Free light-chain; MDE: Myeloma defining events; MGUS: Monoclonal gammopathy of undermined significance; SMM: Smoldering multiple myeloma