A tumor mass composed of myeloblasts or immature myeloid cells. It occurs in extramedullary sites or the bone. (WHO, 2001). The disease is Monarch Disease Ontology entry MONDO_0006861 (myeloid sarcoma). Also known as: chloroma, extramedullary myeloid tumor, extramedullary myeloid tumour, sarcoma, myeloid, malignant.