Ultrastructure of myeloma cells in patients with common acute lymphoblastic leukemia antigen (CALLA)-positive myeloma.

We investigated the ultrastructure of myeloma cells obtained from four cases of common acute lymphoblastic leukemia antigen (CALLA)-positive myeloma. Clinically, the disease was aggressive and our patients died with a median survival after diagnosis of only 62 days. By light microscopic criteria of Greipp et al., their disease was classified as plasmablastic, immature (two cases), and intermediate. In contrast, the myeloma cells of all four cases were judged to be immature and abnormal on the basis of the electron microscopic observation. Characteristic features were sparse heterochromatin, high to moderate nucleocytoplasmic ratio, nuclear bodies, thin and short rough endoplasmic reticula, scattered pattern of mitochondria, and polysomes consisting of five to six ribosomes, along with irregular nuclear membrane, poorly developed organella, and abnormalities in cytoplasmic structures such as dense bodies, vacuoli, buddings, single-sac loop-like structures, multilamellar bodies, and abnormal inclusion bodies. While overlapping each other, it is suggested that the CALLA-positive and the plasmablastic myelomas should be classified separately. Thus, the electron microscopic study, like the immunological marker analysis, provides a useful means for better assessment regarding immaturity and abnormality of myeloma cells.