Minimal residual disease in multiple myeloma.

Multiple myeloma (MM) is a B-cell malignancy in which abnormal, clonal plasma cells proliferate and accumulate in the bone marrow. These abnormal cells, referred to as myeloma cells, disrupt normal bone marrow function and invade bone. Myeloma cells produce and secrete significant quantities of monoclonal protein (M-protein) into the blood and/or urine.1 The clinical features of MM include hypercalcemia, renal failure, anemia, osteolytic bone lesions, and increased susceptibility to infections.2 Nearly all MM cases are preceded by an asymptomatic, pre-malignant, condition known as monoclonal gammopathy of undetermined significance (MGUS) which may progress to a smoldering MM phase.3