Blast crisis supervening on chronic lymphocytic leukaemia. A monoclonal progression of the disease as defined by cell surface markers.

Acute leukaemia is a rare event during the course of chronic lymphocytic leukaemia (CLL), and only a small fraction of such cases have been shown to be true acute lymphoblastic crises. 1 case is described where both small lymphocytes and proliferating lymphoblasts have the same monoclonal pattern as defined by direct immunofluorescence of membrane-bound immunoglobulins. Previous cases are reviewed and do not appear to be mere coincidence: acute blast crisis may represent a part of the natural history of CLL.