Plasma Cell Disorders

Clonal plasma cell disorders (PCDs) encompass a heterogeneous group of distinct entities characterized in common by a clonal expansion and accumulation of plasma cells (PCs) in the bone marrow (BM) and/or other tissues, which is associated in the vast majority of cases with the presence of their product(s) (monoclonal immunoglobulin [Ig], M component) at detectable amounts in serum or urine (1). Although the so-called diseases of immunoglobulin deposits (e.g., primary light chain [AL] amyloidosis) and lymphoplasmacytic lymphoma (e.g., Waldenstrom macroglobulinemia) also belong to this heterogeneous group of disorders, its most representative diagnostic subtypes include monoclonal gammopathy of undetermined significance (MGUS), solitary plasmacytoma, multiple myeloma (MM), plasma cell leukemia (PCL), and several subvariants of these entities (1, 2) (Table 1). The last four diagnostic categories of PCD are the main focus of this chapter.