Myeloid sarcoma of the sternum with regional lymph node involvement in a 6-year-old child: a case report

Myeloid sarcoma is a rare extramedullary tumor composed of myeloid progenitor cells, often associated with acute myeloid leukemia or other hematologic malignancies. Primary involvement of the sternum in children is extremely uncommon and may pose substantial diagnostic challenges. A 6-year-old boy presented with recurrent sternal pain lasting over four months, along with low back pain, bilateral breast pain, and fever. Imaging showed a destructive sternal lesion with an adjacent soft tissue mass, initially raising suspicion for Ewing sarcoma. Bone marrow aspiration demonstrated active hematopoiesis without increased blasts or leukemic infiltration, and leukemia immunophenotyping showed no abnormal leukemic cell population. PET-CT demonstrated a hypermetabolic destructive sternal lesion and a hypermetabolic nodular lesion adjacent to the right internal mammary vessels, without other definite malignant lesions elsewhere in the body. Because the preoperative biopsy yielded limited cellularity and remained inconclusive, surgical resection was performed for definitive diagnosis. Histopathology and immunohistochemistry confirmed myeloid sarcoma. Two resected parasternal lymph nodes also showed tumor involvement. After surgery, the patient was transferred to the hematology department and received induction chemotherapy with the VAH regimen according to the CCLG-AML-2024 protocol. According to the final hematology assessment, the patient was classified as intermediate risk. At the latest documented follow-up in January 2026, complete blood counts remained within normal limits, and chest CT showed no obvious solid mass around the sternum or enlarged mediastinal lymph nodes. Myeloid sarcoma should be considered in the differential diagnosis of pediatric chest masses, even in the absence of overt bone marrow involvement. Accurate diagnosis requires integration of imaging, histopathology, and immunohistochemistry. Surgery plays an important role in diagnostic confirmation and local control, whereas systemic AML-type chemotherapy remains the standard treatment strategy. Early recognition and multidisciplinary management are essential for improving outcomes.