Pure acute erythroblastic leukemia

M6b (Pure erythroid leukemia)In rare cases the erythroid lineage is the only obvious component of an acute leukemia; a myeloblast component is not apparent. The erythroid component consists predominantly or exclusively of proerythroblasts and early basophilic erythroblasts. These cells may constitute 90% or more of the marrow elements. Despite this lack of myeloblasts, these cases should be considered acute leukemias. In a WHO proposal the blastic leukemias that are limited to the erythroid series are designated pure erythroid malignancies.

Erythroblasts are not reactive for MPO, CD34, HLA-DR but are often CD117 dim positive .The immature erythroid elements, normal and dyspoietic, express strongly CD71 (transferin receptor-1). It is expressed in the earliest erythroid precursors, and has been useful for flow cytometry. CD71 is absent in the mature red blood cells in general and is negative in the normal non-erythroid elements as well as in myeloproliferative disorders and nearly all acute myeloid leukemia. Weak CD71 expression is described in acute lymphoblastic leukemia (ALL), diffuse large B-cell lymphoma (DLBCL), and one case of acute megakaryoblastic leukemia but it could be due to a high background stain.
Erythroblasts are also positive for Glycophorin A (GlyA) and hemoglobin A, although there are cases when the blasts are negative for these markers, since they are expressed in more mature cells. Additional markers are used to identify immature erythroblasts such as carbonic anhydrase 1, Gero antibody against the Gerbich blood group or CD36 antibody. CD36 is non-specific and may be expressed in myeloids, monocytes and megakaryoblasts. Spectrin can be also used for evaluation of immature erythroblasts in core biopsies but shows a high background stain.