Radiotherapy for Orbital Myeloid Sarcoma as Extramedullary Relapse in a Pediatric Acute Myeloid Leukemia Patient Post-haploidentical Bone Marrow Transplantation.

The proliferation of immature granulocytic cells characterizes myeloid sarcoma (MS), which can be a rare extramedullary manifestation of acute myeloid leukemia (AML). MS can occur as an isolated lesion, concurrently with AML, or as a post-treatment relapse. In this case report, we describe a 12-year-old male with high-risk AML who underwent chemotherapy followed by haploidentical hematopoietic stem cell transplantation (HSCT). Two years post-HSCT, he experienced a relapse with testicular MS, requiring orchiectomy and radiation therapy. One year later, he experienced a second relapse, with the disease isolated to the left orbit without evidence of systemic disease. Given his prior treatments, chronic graft-versus-host disease, and negative minimal residual disease, radiation therapy alone (2,400 cGy in 12 fractions) was selected to treat the left orbital MS. The dosimetric analysis showed optimal tumor coverage while sparing critical structures. He achieved a complete clinical response with preserved vision. This case highlights the complexities of managing post-HSCT MS in pediatric patients and highlights the role of targeted radiation in localized relapse when systemic therapy is not feasible.