Multiple myeloma.

Abstract

Multiple myeloma (MM) originates from the malignant clonal expansion of transformed B-lymphocytes (in which c-myc and ras oncogenes are probably involved). MM cells have a hybrid phenotype (with coexpression of the markers for both early and late B-differentiation and, sometimes, of T-lymphocyte, myelomonocyte, erythroid and megakaryocyte markers), which accounts for the association between MM and myeloproliferative disorders and for cytokine production. Interleukin-6 and immunologic control mechanisms regulate proliferation and differentiation into plasma cells secreting a monoclonal component (MC). Overt MM is diagnosed 1-2 years following malignant transformation. At this time, several aneuploid clones with resistant phenotype have been selected, and a small pool of actively cycling cells produces the great bulk (over 90%) of non proliferating tumor cells. The clinical and laboratory signs of MM arise from both tumor proliferation and MC damage to organs and organ systems. Tumor proliferation is mainly responsible for bone disease (since MM cells produce cytokines that activate the osteoclasts), inhibition of hemopoiesis and the appearance of plasma cell tumors. The MC causes renal failure, neurological signs, hemorrhagic manifestations. The prognosis for multiple myeloma is probably best estimated by two parameters, serum beta-2-microglobulin and the bone marrow labeling index. Induction therapy is still based on the use of alkylating agents, melphalan and cyclophosphamide, combined with prednisone. Second line treatment consists of VAD polychemotherapy or high-dose pulsed glucocorticoids. Many investigational approaches have been proposed, but their effectiveness awaits confirmation. In the absence of a curative regimen, much effort should be dedicated to the quality of supportive care. In this respect, bisphosphonates represent a new effective tool for the control of myeloma bone disease.