細胞化学的にはＭＰＯ陰性で，免疫細胞化学的には明らかなＭＰＯ陽性反応が認められたＣＤ３４陽性のｈｙｂｒｉｄ ａｃｕｔｅ ｌｅｕｋｅｍｉａの１例

Abstract

A rare case of hybrid acute leukemia is presented. The patient, a 37-year-old man, was admitted to our hospital in September, 1991, suffering from lassitude, fever, lumbago, and slight leukocytosis associated with increased lymphoid blast cells. The bone marrow was remarkably infiltrated by similar blast cells. The blast cells were negative for cytochemical myeloperoxidase (MPO), Sudan black B, non-specific esterase, and specific esterase. MPO activity was not detected in the blast cells even by electron microscopy. Nonetheless, the blast cells were positive for immunocytochemical MPO. A surface marker analysis of the blast cells showed that they were positive for CD13, 19, 33 and 34; that is, the blast cells had both myeloid and lymphoid natures. Moreover, rearranged patterns of immunoglobulin heavy chain gene and T-cell receptor β-chain gene were confirmed in the blast cells. Thus, a diagnosis of hybrid acute leukemia was made. An intensive chemotherapy for acute lymphoblastic leukemia was effective, and a complete remission was achieved. The present case seems rare in the following points. (1) The blast cells possessed both myeloid and T-/B-lymphoid characteristics. (2) Although the blast cells were negative for cytochemical MPO, they were positive for immunocytochemical MPO. This fact suggests that immunocytochemical MPO staining is much more sensitive than cytochemical one, and is useful to detect faint myeloid characteristics.