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Myeloid Sarcoma : Myeloperoxidase

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Myeloperoxidase (MPO) enzyme is responsible for the characteristic greenish hue of some myeloid sarcomas (hence the synonym chloroma; chloros = pale green in Greek). MPO is a major constituent of the primary granules of myeloid cells. Myeloid cells of neutrophilic and eosinophilic types show strong cytoplasmic reactivity for MPO at all stages of maturation by immunohistochemistry. MPO is detected in myeloblasts and immature myeloid cells in a variety of myeloid leukemias.

On the other hand, erythroid precursors, megakaryocytes, lymphoid cells, mast cells, and plasma cells are non-reactive. Cells of monocytic lineage are weakly positive or nonreactive. Various lymphoid neoplasms, epithelial malignancies, and sarcomas are also negative for MPO.

This image shows strong MPO immunoreactivity in a case of myeloid sarcoma presenting as an ovarian mass.

Image courtesy of: Fernando Bolanos, MD, Colombia; used with permission.

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