The most obvious feature of myeloma patients is the abnormal quantity and quality of plasma cells. Typically, plasma cells are greater than 15%, and myeloma cells appear in a disproportionate pattern. Typical tumor cells are immature, poorly differentiated plasma cells with a multinucleated rounded or irregular morphology, with nuclear membranes invaginated, and vacuoles visible within the nucleus; yeast cells are usually seen in surgical cases, and yeast cell myeloma is an independent indicator of a poor prognosis. Pathologically, in bone marrow and extramedullary tissues, plasmacytomas can present as nodular or sarcomatoid proliferations. Bone marrow biopsy is more reflective of the extent of plasma cell infiltration in the bone marrow than bone marrow pictures.