Terminal Transferase Expression in Relapsed Acute Myeloid Leukaemia

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Abstract
In 3 [human] cases of acute myeloid leukemia marked increases in expression of the nuclear enzyme, terminal deoxynucleotidyl transferase (TdT), were observed during disease relapse. The 1st case was heterogeneous at diagnosis, consisting of subpopulations of large TdT- myeloblasts and small TdT+ blasts; at relapse there was complete replacement by TdT+ lymphoblasts. The other cases at diagnosis were both typical acute myeloid leukemia, TdT-; at relapse, showed a mixture of TdT- myeloblasts and TdT+ lymphoblasts, while in the other, TdT was demonstrated on a subpopulation of myeloblasts. No chromosomal abnormalities were found. In the 1st 2 cases there phenomena may have been due to leukemic involvement of a pluripotential stem cell, or that sub-clones with different properties may have coexisted. In the 3rd case at relapse, TdT was expressed aberrantly by malignant myeloid cells.