A diverse group of diseases characterized by the proliferation of a single clone of cells producing a monoclonal immunoglobulin or immunoglobulin fragment (a serum M component). The cells usually have plasma cell morphology, but may have lymphocytic or lymphoplasmacytic morphology. This group includes multiple myeloma, Waldenström macroglobulinemia, the heavy chain disease, benign monoclonal gammopathy, and immunocytic amyloidosis.
Medical dictionary. 2011.