Acute myeloid leukemia with minimal differentiation. A multiple parameter study.

Acute myeloid leukemia with minimal differentiation (AML-M0) is a recently described entity, and few large studies are available to characterize its clinical and pathologic features. We reviewed blood and bone marrow morphology, cytochemistry, immunophenotyping, and cytogenetics, as well as the clinical findings, of 17 patients with AML-M0. Most patients were male, with a median age of 62 years. Minimal background myelodysplastic features were identified in only 5 of 15 patients. Cytochemical stains for myeloperoxidase and alpha-naphthyl butyrate esterase were negative in the leukemic blasts of all specimens. Positivity for one or both myeloid-associated antigens, CD13 and CD33, was seen in all patients. Both CD34 and HLA-DR were positive in all tested cases. Lymphoid-associated antigens were identified in seven patients; these antigens were typically dim or weak in intensity. Terminal deoxynucleotidyltransferase positivity was seen in 14 of 14 tested patients; monoclonal anti-myeloperoxidase reactivity was seen in the blasts of 2 patients. Abnormal clonal karyotypes were found in 6 of 14 patients. Abnormalities of chromosomes 7 and 13 were the most common findings, most frequently manifested by monosomy 7 and trisomy 13. The median follow-up was 8 months. Eight patients died of their disease, three are alive with disease, and six are in first or second remission (including three patients treated with bone marrow transplantation). When narrowly defined, AML-M0 appears to be a homogeneous entity that affects older and predominantly male patients. It has no single karyotypic abnormality, but complex karyotypes with monosomy 7 and trisomy 13 are commonly found. Acute myeloid leukemia with minimal differentiation is relatively resistant to chemotherapy; however, bone marrow transplantation may provide a better outcome for eligible patients.