Clinical characteristics, molecular profile and outcomes of myeloid sarcoma: a single institution experience over 13 years.

Background: Myeloid sarcoma (MS) is characterized by extramedullary infiltration by immature myeloid cells. Owing to rarity of this disease, the clinical features and overall outcomes are yet to be clarified. Objective: To define clinical characteristics, epidemiology, pathologic findings, treatment options and outcomes in MS. Methods: We conducted a retrospective review of 23 patients diagnosed with MS at our institute over a period of 13 years (2002-2015). Results: MS presented mostly as a manifestation of relapsed acute myeloid leukemia, seen in 39% of patients. Skin and subcutaneous soft tissues were the most common sites of anatomic involvement (69.5%). Ninety five percent (n = 19) were positive for classical myeloid markers with either cytochemical staining (chloracetate-esterase, MPO), flow-cytometry (CD33, CD34, CD13 and CD117), or immunohistochemistry (CD34, CD43, CD68 and lysozyme). Of these, 52% were positive for CD33 (n = 12), 35% for CD68 (n = 8), 30% for CD34 (n = 7), and 26% for lysozyme (n = 6). Cytogenetic abnormalities were seen in 63% (n = 12/19) patients on bone-marrow aspirate, with five patients displaying a complex (n = 3) or monosomal (n = 2) karyotype. Twenty seven percent patients with a normal karyotype had presence of deleterious mutations (FLT3, ASXL, STAG and JAK2) on further testing with myeloid mutation panel. The Median overall survival (OS) of the entire cohort was 15.9 months (95% CI, 7.4-24.4 months). The OS was significantly better for patients < 65 years (24.6 vs. 3.4 months, p = 0.009) of age, and for those attaining a complete remission (CR) to induction therapy (25.7 vs. 0.8 months, p < 0.001). All patients who underwent allogeneic hematopoietic stem cell transplant attained long-term remissions, with a median follow-up of 54 (range 32-120) months. Conclusion: Failure to achieve CR with induction therapy, and age > 65 years are associated with poor outcomes in MS. Allogeneic stem-cell transplant in first remission appears to be the most effective modality for achieving long-term remissions.