Adult hypocellular acute leukaemia with lymphoid differentiation.

The rare hypocellular variants of acute leukemia (AL) previously also termed smouldering leukemia, almost always exhibit myeloid differentiation. Very rare cases of hypocellular AL with lymphoid differentiation have been reported, usually in children. This paper describes two cases (an 87-year-old woman and a 79-year-old man) in whom the blood findings were suggestive of AL. Paraffin-embedded bone marrow biopsy specimens revealed similar findings in both patients: there was severe hypocellularity, the cells of normal hemopoiesis were greatly reduced in number, and there was a diffuse increase in blast cells, which represented more than 50% of nucleated marrow cells. The blasts coexpressed TdT and CD34 and were negative for myeloperoxidase, CD117, CD68 and naphthol AS-D chloroacetate esterase. For the first time immunohistochemical Pax-5/CD34 doublestainings are provided, which revealed the blasts in one case to coexpress Pax-5 and CD34. All the blasts were CD79a-positive and 20% were also CD10-positive. In the other case, 20% of the blasts were CD79a-positive, 30% coexpressed Pax-5 and CD34 by doublestaining, and showed a clonal rearrangement of the immunoglobulin heavy chain gene. Thus a diagnosis of AL of lymphoid lineage, hypocellular variant, was made on the basis of immunohistochemical findings. The clinical course appears to be similar to that of hypocellular AML, as neither patient has developed overt leukemia during the one-year follow-up period.