Diagnosis and staging

Multiple myeloma (MM) is a plasma cell disorder characterized by a clonal proliferation of cells producing a homogeneous plasma protein of monoclonal character (M-protein or paraprotein), restricted by kappa or lambda light chains, which are detected in the serum and/or urine [1]. In fact, MM is the prototypical malignant monoclonal gammopathy, where the amount of paraprotein produced by the plasma cell proliferation and immunodeficiency gives rise to the clinical and biological features of the disease. Diagnostic criteria from the International Myeloma Working Group include clonal bone marrow plasma cells ≥10 %, the presence of serum and/or urinary monoclonal protein (except in patients with nonsecretory multiple myeloma), and evidence of end-organ damage, which can be attributed to the underlying plasma cell proliferative disorder [2].