Plasma cell myeloma is a clonal proliferation of immunoglobulin-producing plasma cells that usually presents as destructive tumors involving the axial skeleton. The bones most commonly affected include vertebral column, ribs, skull, pelvis, femur, proximal humerus, clavicle, and scapula. The lytic bone lesions range in size from 1 to 4 cm and are filled with soft, gelatinous, red-brown tumor. This photograph shows multiple round lytic lesions involving the skull of a 60 y/o male with plasma cell myeloma. Image copyright: pathorama.ch.