Acute lymphoblastic leukemia with azurophilic granules that contain ultrastructural myeloperoxidase activity.

We present a case of acute lymphoblastic leukemia (ALL) in which the leukemic cells had cytoplasmic azurophilic granules. Surface marker studies revealed that the leukemic cells expressed CD10 (CALLA), CD19, CD20, and HLA-DR antigens. Cytochemical studies by light microscopy revealed that the blasts were negative for myeloperoxidase, PAS staining, and double esterase staining, supporting the diagnosis of ALL. However, an ultrastructural study demonstrated that some of the cytoplasmic granules were myeloperoxidase (MPO) positive. Our findings suggested that leukemic transformation in this case may have taken place at a stage ontogenetically close to the pluripotent stem cell. Furthermore, the present case indicates the existence of a new form of ALL is characterized by MPO-positive granules detectable by ultracytochemistry and lymphoid-associated surface markers.