Abstract

Leukemia cutis (LC) and reactive myeloid infiltrates in the skin can be indistinguishable histologically even after an extensive ancillary study work-up. This poses a serious clinical dilemma, as the prognosis and treatment of these conditions are markedly different. Erythroblast transformation specific regulated gene-1 (ERG) is a member of the erythroblast transformation specific family and is a key regulator of cells proliferation, differentiation, angiogenesis, inflammation, and apoptosis. ERG has been recently reported to be overexpressed in acute myeloid and lymphoblastic leukemia. We report a case of a 51-year-old female with history of acute myeloid leukemia, in remission ten years status post allogenic peripheral blood stem cell transplant, who presented with an exquisitely tender scalp lesion. Punch biopsy showed a dermal perivascular and peri-adnexal infiltrate with scattered atypical and immature-appearing cells which extended to involve the subcutis. By IHC these atypical cells were positive for lysozyme, CD4 (subset), CD43 (subset), CD117 and MPO (small subset), while negative for CD56, CD34 and dim CD117 expression. ERG was diffusely positive in neoplastic cells. LC was considered in the differential diagnosis. Molecular studies revealed pathogenic IDH2, KRAS, NPM1 and U2AF1 mutations which further supported diagnosis of myeloid sarcoma. This case highlights ERG as helpful marker in the diagnosis of LC in challenging cases.

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