HLA-Dr negative acute non-lymphocytic leukemia.

Absent or diminished HLA-Dr antigen representation on the cell surface of both normal and leukemic promyelocytes is a hallmark of this stage of myeloid maturation. In order to document the specificity of this finding for acute promyelocytic leukemia, flow cytometric analysis of leukemic blasts was utilized on 36 cases of acute non-lymphocytic leukemia. All 15 of the promyelocytic leukemias (FAB-M3) studied showed absent or markedly decreased HLA-Dr antigen on their cell surface. However, the majority of cases (21) in which this finding was noted were other than promyelocytic leukemias and included all FAB subtypes, most particularly FAB-M2, i.e., myeloblastic leukemia with maturation. It is concluded that absent to decreased HLA-Dr antigen representation on leukemic blasts lacks specificity and can be seen in all acute myeloid/monocytic leukemic subtypes.