Rhabdomyosarcoma Confined to the Bone Marrow: A Case Report and Literature Review.

Rhabdomyosarcoma (RMS) confined to the bone marrow represents an exceptionally rare and aggressive presentation that can mimic primary hematological malignancies, often leading to diagnostic delays and therapeutic challenges. We report the case of a 34-year-old woman who presented with clinical and laboratory findings highly suggestive of a hematological disorder, including cytopenias and diffuse bone marrow involvement. Initial evaluation raised suspicion for leukemia; however, comprehensive diagnostic work-up, including immunohistochemistry and molecular studies, ultimately confirmed the diagnosis of PAX3/FOXO1 gene-rearranged alveolar RMS isolated in the bone marrow, with no identifiable primary soft tissue mass. The patient was treated with an intensive multi-agent chemotherapy regimen, resulting in a marked hematological recovery and a significant radiological improvement after a limited number of cycles. We further reviewed the limited literature on bone-marrow-confined RMS, highlighting the proposed pathophysiological mechanisms, diagnostic pitfalls, and reported treatment strategies. Given the absence of standardized management guidelines for this rare entity, therapeutic approaches are often extrapolated from conventional RMS protocols or regimens used for high-grade sarcomas. Our experience supports the potential efficacy of intensive chemotherapy in achieving meaningful clinical responses. This case report emphasizes the challenges in the diagnosis of RMS confined to the bone marrow due to its atypical presentation. It also highlights the poor prognosis and aggressiveness of this entity compared to conventional RMS.