Acute biphenotypic leukaemia (myeloid and null-ALL type) supervening in a myelodysplastic syndrome.

An acute leukaemia was seen in a 72-year-old patient with a myelodysplastic syndrome (MDS) of 14 months duration, who had been treated only with steroids. The morphological appearance of the blast cells suggested a poorly differentiated cell type. Surface marker analysis, including double staining studies, showed the coexistence of a population of null acute lymphoblastic leukaemia (ALL) blast cells together with acute myeloid leukaemia type cells. No chromosomal alterations were detected. The change from a chronic MDS to an acute leukaemia of mixed (myeloid and null ALL) type suggests either transformation of a pre-existing abnormal clone or de novo appearance of two separate leukaemic clones.