Myeloid sarcoma of the cheek and the maxillary sinus regions.

Myeloid sarcoma (MS) is a rare, extramedullary malignant tumor composed of immature myeloid precursor cells and myeloblast. Most MSs occur in the subperiosteal region of the bone, with the skull, sternum, ribs, and proximal portions of the long bones being the common sites of involvement. It is thought that the MS tumor originates in the bone marrow, and traverses the Haversian canals to reach the subperiosteum. Various reports have also described the involvement of the liver, spleen, brain, heart, pharynx, uterus, vagina, skin, kidney, and other soft tissues in the formation of the tumor.