The Outcomes of Myeloid Sarcoma in 64 Pediatric Patients and the Impact of Allogeneic Hematopoietic Stem Cell Transplantation on Treatment Results

<b>Background:</b> Myeloid sarcoma (MS) is a malignant extramedullary tumor that occurs in patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or chronic myeloid leukemia (CML). The standard first-line treatment for MS is intensive chemotherapy according to the AML protocol, regardless of bone marrow involvement. The role of allogeneic hematopoietic stem cell transplantation (alloHSCT) in the treatment of pediatric patients with MS requires further investigation. The aim of the study was to evaluate treatment outcomes for MS in pediatric patients with a focus on assessing the impact of allogeneic hematopoietic stem cell transplantation (alloHSCT) on treatment efficacy. <b>Material and Methods:</b> The study included 64 patients aged 0 to 19 years from 15 pediatric oncology centers in Poland who were diagnosed with MS between 1998 and 2024. An Excel database was created to collect data on clinical features and treatment methods and outcomes. <b>Results:</b> The probability of 5-year overall survival (pOS) for the entire cohort was 0.63 ± 0.07, while the 5-year event-free survival (pEFS) and 5-year relapse-free survival (pRFS) were 0.62 ± 0.07 and 0.72 ± 0.07, respectively. Treatment outcomes were compared between patients who underwent allogeneic hematopoietic stem cell transplantation (alloHSCT) in first complete remission (ICR) (n1 = 17/64; 27%) and those who did not receive alloHSCT (n2 = 47/64; 73%). In the alloHSCT group (n1), the estimated survival probabilities were pOS = 0.49 ± 0.13, pEFS = 0.44 ± 0.14, and pRFS = 0.40 ± 0.14. In the non-alloHSCT group (n2), these values were pOS = 0.68 ± 0.08, pEFS = 0.68 ± 0.08, and pRFS = 0.84 ± 0.06. The difference in pRFS between groups n1 and n2 was statistically significant (<i>p</i> = 0.0049). Extramedullary relapses were more frequently observed in patients who had undergone allogeneic hematopoietic stem cell transplantation (alloHSCT) (<i>p</i> = 0.0001). <b>Conclusions:</b> Allogeneic hematopoietic stem cell transplantation (alloHSCT) does not improve the outcome of patients with MS. Further research is needed to identify effective strategies for sustaining remission in patients with MS after alloHSCT.