Survey of ERG expression in normal bone marrow and myeloid neoplasms

The immunohistochemical stain ERG is a useful diagnostic marker for leukemia cutis. Translocations involving the ERG gene have been identified in acute myeloid leukemia (AML) and it plays critical roles in differentiation of hematopoietic stem cells. However, little is known about ERG expression in the bone marrow or in myeloid neoplasms. The aim of this study is to characterize ERG expression in normal bone marrow specimens, and those with various myeloid neoplasms. We performed immunohistochemical studies assessing ERG expression in bone marrow biopsies obtained over a 1-year period, in which myeloperoxidase (MPO) was used to assess granulocyte populations. Twenty-eight bone marrow biopsies (6 normal, 12 with acute myeloid leukemia (AML), 6 with myeloproliferative neoplasms (MPN), and 4 with myelodysplastic/MPN) were identified. Strong nuclear ERG staining was present within the granulocytes and precursors in near complete concordance with MPO in 26/28 (93%) cases. Fifty-eight percent of AML cases showed more staining for ERG than MPO in the leukemic cells. ERG can be useful for assessing granulocyte populations in bone marrow biopsies, and in many instances of AML, stained a proportion of myeloblasts.