Acute myeloid leukemia with monocytic differentiation (myeloid sarcoma) masquerading as bone-soft tissue malignancy

Abstract Introduction/Objective Myeloid sarcoma is an extramedullary solid neoplasm composed of myeloid precursors with or without maturation. This tumor usually occurs simultaneously or following the onset of acute leukemia. Rarely, it can be the first manifestation of acute myeloid leukemia. We report a case of this rare tumor presenting histologically as a bone sarcoma with features of extraskeletal myxoid chondrosarcoma and myoepithelial carcinoma Methods/Case Report A 76-year-old female was referred to our institution for evaluation of a right foot mass associated with pain and swelling. MRI showed a 2.4 x 1.5x 1.2 cm soft tissue mass along the lateral margin of proximal and mid diaphysis of first metatarsal. The clinical and radiologic differential diagnosis was primary bone-soft tissue malignancy, or infection. Histologically, the biopsies showed sheets and cords of cells in a myxoid background. Cytologically the cells were plasmacytoid, mononuclear, mitotically active with immature chromatin, prominent nucleoli, and moderate to abundant cytoplasm. This morphologic appearance elicited the differential diagnosis of extraskeletal myxoid chondrosarcoma, myoepithelial carcinoma, and plasmacytoma. An initial panel of immunohistochemical stains showed the lesional cells to be negative for S-100, SOX-10, pancytokeratin, desmin, p63, EMA, CAM5.2, and CD138 but positive for CD43. Additional immunohistochemistry showed diffuse reactivity for CD33, and lysozyme; CD163 was focally positive, and the cells were negative for CD20, CD3, CD30, CD99, MUM1, CD138, and CD34. A diagnosis of extramedullary acute myeloid leukemia with monocytic differentiation (myeloid sarcoma) was rendered. Subsequently, patient underwent bone marrow biopsy which showed involvement by acute myeloid leukemia with monocytic differentiation. Results (if a Case Study enter NA) NA Conclusion Myeloid sarcoma is a rare tumor and presentation as an isolated metatarsal mass is highly unusual and exceedingly rare. This can mislead clinicians, radiologists, and pathologists. Pathologists need to keep hematopoietic tumors in their differential diagnosis even when the anatomic sites as well as the morphology are not typical of hematopoietic malignancies.