V. Smoldering multiple myeloma.

Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell disorder defined in 1980 by Kyle and Greipp on the basis of a series of six patients who met the criteria for multiple myeloma (MM) but whose disease did not have an aggressive course [1]. At the end of 2014, the International Myeloma Working Group (IMWG) updated the definition, and SMM is now defined as a plasma cell disorder characterized by the presence of one or both of the features of ≥3g/dL serum M-protein and 10–60% bone marrow plasma cells (BMPCs), but with no evidence of myeloma-related symptomatology (hypercalcemia, renal insufficiency, anemia or bone lesions (CRAB)) or any other myeloma-defining event (MDE) [2]_ENREF_2. According to this recent update, the definition of SMM excludes asymptomatic patients with BMPCs of 60% or more, serum free-light chain (FLC) levels of ≥100, and those with two or more focal lesions of the skeleton as revealed by magnetic resonance imaging (MRI). Kristinsson et al., through the Swedish Myeloma Registry, recently reported that 14% of patients diagnosed with myeloma had SMM and, taking the world population as a reference, that the age-standardized incidence of SMM was 0.44 cases per 100 000 people [3].