Acute unclassified leukemia: A clinicopathologic study with diagnostic implications of electron microscopy

By rigid cytological and cytochemical criteria, the diagnosis of acute and undifferentiated leukemia was established in 22 patients. According to defined criteria, the leukemic cells could not be classified by conventional light microscopic techniques employed in the study of hematopoietic tissue. Cytochemical studies including peroxidase, periodic acid schiff (PAS) and nonspecific esterase (alpha napthyl butyrate-reacting esterase) stains were done on fresh bone marrow samples, and the percentage of positive leukemia cells for each of these stains was determined on 200 cells. In this series of leukemias, cytochemistry at the light microscope level did not contribute to further classification. Subsequent electron microscopic examination of bone marrow samples from these patients confirmed the immaturity and nuclear/cytoplasmic asynchrony of the leukemic cells. Several in vivo neoplastic markers, such as nuclear blebs, increased nuclear bodies, and cytoplasmic fibrillar bundles could be demonstrated in these cells. Fourteen cases from this series exhibited peroxidase-positive developmental granule formation at the ultrastructural level and were reclassified as acute granulocyte leukemia (AGL). One case was reclassified as lymphoma (poor differentiated type), one case was diagnosed as acute monocytic leukemia (AmonoL), and six cases remained in the undifferentiated category (AUL). Clinical and laboratory features, response to treatment, and survival data were evaluated for these patients. This study demonstrated that electron microscopy is useful in the cytological diagnosis of human leukemia.