Ultrastructural characterization of de novo and secondary leukemias.

Cells from 95 patients with acute leukemia were studied by cytochemistry, light microscopy, and transmission electron microscopy (TEM), and were classified according to the French-American-British (FAB) guidelines. This group included 63 patients with acute nonlymphocytic leukemia (ANLL) de novo, 18 with acute lymphocytic leukemia (ALL), and 14 with ANLL as a second malignancy. In addition, 13 cases of chronic myelocytic leukemia in blast crisis were studied. Ultrastructural examination resulted in reclassification of 6 cases of ANLL de novo; two of these were reclassified from M2 (myeloblastic leukemia with maturation) to M3 variant (microgranular variant of hypergranular promyelocytic leukemia). The classification of the cases of CML in blast crisis was identical by light microscopy and TEM. IN 1 case of myeloblastic crisis, however, basophilic granules were demonstrated by TEM but were not appreciated by light microscopy. Classification of the cases of secondary leukemia was possible by light microscopy and cytochemistry in all 14 cases, but was often difficult since the cytochemical reactions were usually less intense than in de novo ANLL. This was particularly true in those cases classified as M1, and in such cases, TEM was required to confirm the diagnosis.