Alexandre da Silva Faco Junior

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.

Maintenance chemotherapy prolongs progression-free survival (PFS) in several malignancies, but its role in soft tissue sarcoma (STS) remains unclear. Conventional doxorubicin is limited by cumulative toxicities. Liposomal doxorubicin may allow prolonged therapy. We evaluated outcomes of patients treated with maintenance liposomal doxorubicin following induction doxorubicin. This was a single-center retrospective study using the Quebec Sarcoma Registry from 2015 to 2025. Eligible patients had histologically confirmed STS and received doxorubicin-based induction therapy. Those achieving disease control were treated with maintenance liposomal doxorubicin. Clinical variables, adverse events, and outcomes were collected, and PFS and overall survival (OS) were estimated using the Kaplan–Meier method. Twenty-four patients were included (median age 61 years; 62.5% male), with leiomyosarcoma and undifferentiated pleomorphic sarcoma as the most frequent histologies. The median induction exposure was six cycles, and maintenance treatment was administered for a median of five cycles. Median PFS was 11.4 months, and median maintenance PFS was 6.1 months. Infusion reactions and hematologic toxicities were the most common adverse events. Median OS was 60.2 months. Maintenance liposomal doxorubicin was feasible, well-tolerated, and associated with encouraging disease control in selected patients, supporting further prospective evaluation.