Redefining plasma cell leukaemia

Plasma cell leukaemia is an aggressive plasma cell malignancy characterised by the presence of a high percentage of circulating clonal plasma cells on conventional peripheral blood smear examination. We argue that plasma cell leukaemia must no longer be considered as a separate disease entity but as a type of high-risk multiple myeloma. With the adoption of more strict criteria for defining high-risk multiple myeloma and the relaxation of criteria in defining plasma cell leukaemia, the clinical implications of the terms have converged. Circulating plasma cells-the defining feature of plasma cell leukaemia-are present in almost all patients with multiple myeloma. Thus, the term plasma cell leukaemia merely reflects the high end of a continuum, with the main difference being a quantitative arbitrary threshold based on the percentage of circulating plasma cells. One of the key drivers of our proposal is to make progress against this aggressive malignancy, and to include such patients in clinical trials for multiple myeloma. The term plasma cell leukaemia creates substantial confusion and concern to patients, and it is time for a change. Finally, we provide counterarguments to our proposal and highlight the need to harmonise these proposed changes in disease definitions used by health organisations.