ACUTE MYELOBLASTIC-LEUKEMIA WITH MINIMAL MYELOID DIFFERENTIATION - PHENOTYPICAL AND ULTRASTRUCTURAL CHARACTERISTICS

AML-MO is an infrequent form of acute myeloblastic leukemia characteri zed by negative reaction with myeloperoxidase (MPO), Sudan Black and l ymphoid antigens and positivity for CD13 or CD33. In the present study we describe the immunophenotypical and ultrastructural characteristic s of a group of AML-MO in adult patients. Nine out 218 AML leukemias ( 4.1%) fulfilled the AML-MO criteria. CD13 or CD33 were positive in eig ht out nine cases, with two or more positive myeloid antigens being pr esent in 82% of the cases. Immunological MPO was positive in 57% of th e cases and CD68 in 33%. In no case were megakaryocytic and erythroid markers present. Four cases (44%) expressed CD7 and TdT but only two c oexpressed both antigens. In none of the cases was CD3 or CD22 cytopla smic expression found. Ultrastructurally, a low number of granules was seen in all cases whereas ferritin particles or rhopheocytosis were n ot observed. Ultrastructural MPO was positive in one out of five cases and platelet peroxidase (PPO) was negative in the four cases studied. Two out of six cases showed karyotypic abnormalities (hypotetraploidy and a complex karyotype, respectively). In two out three cases a rear ranged pattern for J(H) gene was observed. TCR (C beta and J gamma) re arrangements were not detected in any case. AML-M0 is an infrequent fo rm of acute myeloblastic leukemia. A large panel of myeloid monoclonal antibodies (MoAb) and the study of the cytoplasmic expression of myel oid antigens is necessary to diagnose this form of leukemia. AML-M0 us ually coexpress lymphoid markers. Ultrastructural studies may be of he lp to discard an immature erythroid proliferation.