Case report: Orbital myeloid sarcoma: a report of two rare cases and review of the literature.

Myeloid sarcoma (MS) occurs when primitive or naive myeloid cells form outside the bone marrow. It occurs mainly in soft/connective tissue and skin; orbital involvement is rare. We report the cases of two female adults, analyze the clinicopathologic characteristics, and review the literature. The average age of both patients was 28 years and they presented unilateral proptosis combined with varying degrees of impaired visual acuity and restricted ocular motility in the affected eye. Despite this, they maintained good overall health and no notable family history. However, the patients had no systemic clinical manifestations of acute myeloid leukemia (AML). Both patients underwent surgical resection of the orbital tumor. Immunohistochemistry showed positive staining for CD43, Leukocyte Common Antigen (LCA), and myeloperoxidase (MPO) and a high level of positive staining for Ki67, which were diagnostic for MS. Bone marrow cytology examination showed no apparent abnormalities. Postoperative chemotherapy, local radiotherapy, and allogeneic hematopoietic stem cell transplantation (allo-HSCT) were performed in Case 1, while the second patient underwent adjuvant chemotherapy and radiotherapy. No recurrence or metastasis was found in either patient during follow-up (one more than 5 years, the other more than 10 years). The occurrence of orbital MS is infrequent, with atypical clinical and imaging findings. The diagnosis depends on pathomorphology and immunohistochemical staining, and the prognosis is good with postoperative adjuvant chemotherapy, local radiotherapy, and allo-HSCT.