2. Epidemiology

MS can manifest under different clinical scenarios including, (1) MS with concurrent AML, (2) as an isolated tumor and may precede the blood and bone marrow involvement or without any history of myeloid neoplasia and, (3) extramedullary relapse of AML [1, 3, 6–9]. However, with a limited number of prospective studies, the exact frequency and the extent of MS are not well described. Based on the retrospective and the autopsy studies, the occurrence of MS in AML patients is reported to be 10% across genders and all age groups [3, 10, 11]. In depth analysis however revealed that MS primarily affects pediatric patients (>50% of all MS patients) with slight male biasness [7, 12, 13]. In 15–35% of cases, MS can appear concomitantly with AML, whereas, in 50% of cases MS appears following the diagnosis of AML. In rare instances (<1%), MS has also been diagnosed after allogenic stem cell transplantation (allo-SCT), which manifests as an isolated tumor with or without accompanying blood and bone marrow relapse [14, 15].
