Hybrid leukaemia of T cell and myeloid lineages: cytogenetic distinction from second (induced) malignancy

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Abstract
The therapeutic and prognostic implications of relapse and clonal evolution of leukaemia are substantially different from those of secondary (induced) malignancy. This report documents the case of a patient who presented with apparent acute non-lymphocytic leukaemia (ANLL) following therapy for acute (T-cell) lymphoblastic leukaemia (ALL) 4 years previously. Morphologically and cytochemically the cells were of myeloid type, but the cell markers showed a T cell lineage. Cytogenetic studies confirmed that this was a relapse of T cell ALL with a phenotypic change, rather than a second malignancy induced by chemotherapy. A 14q deletion present at initial diagnosis recurred at relapse, with the addition of cells with complete deletion of chromosome 14, indicating clonal evolution.