MYOM2 and plasma cell myeloma: While myeloma is characterized by monoclonal plasmacytosis of the bone marrow, with or without bone destruction, and by the presence of M-protein in urine or in serum, in SP there is no evidence of significant bone marrow plasmacytosis and less than 30% of subjects with SP have M-protein, and when it is present it is low compared to the level in myeloma [3,7,8].