Questions concerning plasma cell leukaemia.

The classical concept of plasma cell leukaemia (PCL) is reviewed. This disease invariably concerns myeloma, either in its terminal phase (secondary PCL) or particularly rapid and aggressive (primary PCL). A more precise definition of primary PCL would be given by the term leukaemic myelomatosis. Characterization of the membrane antigen CD 56, responsible for the cytoadhesion of malignant plasmocytes in the bone marrow, today offers a convincing pathogenic hypothesis to elucidate this affection which would now appear to be no more than a variant form of myeloma. Acute immunoblastic-plasmoblastic leukaemia and mature cell leukaemic lymphoma would seem to be pathologically related to PCL. Finally, the problems posed by the "enigmatic" plasmacytoid monocyte are discussed.