Myeloid sarcoma (myelosarcoma) represents a rare malignant tumour arising by extramedullary or bone tumour mass forming neoplastic proliferation of myeloid cells at different stages of their differentiation. It is usually associated with some clonal myeloproliferative disease – most often with some of acute myeloblastic leukemia types – and the extramedullary manifestation might be primary („de novo“) or secondary. The diagnosis of myelosarcoma is defined by a complex of morphologic, immunohistochemical, cytogenetical, and clinical parameters. However, all these parameters are individually heterogenous what might negatively influence the correct diagnosis and appropriate treatment selection. The paper includes an integration of recent information about the definition, typing, grading, biologic manifestation and prognosis of myeloid sarcoma.

        Key words: myeloproliferative disease, myeloid sarcoma (myelosarcoma), acute myeloblastic leukemia