Abstract
One hundred and forty cases of myeloma were reexamined histologically and classified in three histocytological grades. Close correlations were established between the clinical stages as defined by Durie and Salmon (1975) and the grades of histocytological differentiation. The number of osteolytic lesions correlates with dedifferentiation of malignant plasma cells. Dedifferentiation and high plasma cell counts in the bone marrow are associated with rarefication of hemopoiectic cells and often with an increase of reticular fiber network.