Prevalence, incidence and survival of smoldering multiple myeloma in the United States

Smoldering multiple myeloma (SMM) is currently defined as MM without evidence of impending ( ⩾ 60% clonal bone marrow plasma cells, serum involved to uninvolved free light chain ratio of ⩾ 100 with absolute involved light chain level of ⩾ 100 mg/L, or >1 focal lesion on magnetic resonance imaging ⩾ 5 mm in size) or active (hyper c alcemia, r enal insufficiency, a nemia or b one lesion – crab signs) end organ damage, which are considered indications for treatment. 1 Although institutional studies show that ~8–20% of patients with MM are smoldering at the time of diagnosis, 2 the actual prevalence of SMM in the United States (US) is unknown. Epidemiologic studies have been difficult to perform due to the lack of International Classification of Diseases (ICD) codes differentiating smoldering from active MM.