Frequency and Distinct Characteristics of Acute Myeloid Leukemia Lacking HLA-DR and CD34 Expression: Features Intermediate between Typical Acute Myeloid Leukemia and Acute Promyelocytic Leukemia

ABSTRACT

BACKGROUND: The objective of this study was to investigate the frequency and characteristics of HLA-DR⁻/CD34⁻ acute myeloid leukemia (AML) also known as acute promyelocytic leukemia (APL)-like AML. METHODS: This study included 683 newly diagnosed patients with AML. After exclusion of 211 patients with recurrent genetic abnormalities, one with acute panmyelosis with myelofibrosis, two with myeloid leukemia associated with Down syndrome, and two devoid of metaphase cells, we classified the remaining 467 patients as follows group 1, HLA-DR⁺/CD34⁺ (typical AML); group 2, HLA-DR⁺/CD34⁻ or HLA-DR⁻/CD34⁺; group 3, APL-like AML. RESULTS: Group 1 comprised 294 patients, group 2 comprised 133, and group 3 comprised 40. Therefore, the frequency of APL-like AML among 683 unselected patients with AML was 5.9%. Group 3 patients had significantly higher leukocyte counts and bone marrow (BM) blast percentages, higher frequencies of normal karyotypes and NPM1 mutation, higher fractions of CD33-positive cells, higher concentrations of fibrin degradation products and D-dimers, lower frequencies of complex karyotypes, monosomal karyotypes and poor cytogenetic risk, lower fractions of CD13-positive cells, and lower fibrinogen concentrations, compared with group 1 patients. The values of the BM blast percentage, number of CD33-positive cells, and DIC score of the patients with APL-like AML were intermediate between those of the patients with typical AML and APL. CONCLUSIONS: This study demonstrates that APL-like AML is not uncommon, and it has characteristics distinguishable from those of typical AML. APL-like AML may have some pathophysiological relationships with APL, which need further investigation.