The development of acute myelomonocytic leukemia in a patient with acute lymphocytic leukemia

A diagnosis of acute lymphocytic leukemia (ALL) was made from a peripheral blood and bone marrow specimen from a 59-year-old woman. Typical-appearing lymphoblasts were positive for periodic acid-Schiff (PAS) reaction, but negative for peroxidase, Sudan black B (SBB) and non-specific esterase (NSE) stains. Lymphoblasts failed to form non-immune rosettes and had no surface membrane immunoglobulins. However, lymphoblasts exhibited an "Ia-like" membrane antigen and markedly stimulated allogeneic lymphocytes in a mixed lymphocyte reaction (MLR). These cytochemical and immunologic studies were considered characteristic of null-cell subtype of ALL. Thirteen months later, the peripheral blood and bone marrow specimens contained numerous myelomonoblasts characterized by a weak or negative PAS stain and strongly positive peroxidase, SBB, and NSE reactions. Electron micrographs of the bone marrow suggested that the majority of leukemic cells were myelomonocytic and a minority of cells were lymphoblasts. In addition, myelomonoblasts in liquid cultures appeared to differentiate into mature macrophages. These data suggest the development of acute myelomonocyte leukemia in a previous case of ALL.