Clear Cell and Histiocytic/Dendritic Cell Sarcomas: Clinical Outcomes, Molecular Features, and Diagnostic Pitfalls.

Background: Dendritic and histiocytic cell sarcoma (DHCS) and clear cell sarcoma (CCS) are ultra-rare soft-tissue sarcomas characterized by diagnostic ambiguity, limited treatment guidelines, and poor outcomes. Their rarity has restricted the development of evidence-based management strategies, leaving clinical decisions reliant on small case series and institutional experience. DHCS typically presents without a unifying molecular driver and is often misclassified without comprehensive immunophenotyping. CCS is defined by EWSR1-ATF1/CREB1 fusions but exhibits low responsiveness to conventional chemotherapy. There remains a clear need to clarify natural history, therapeutic responses, and molecular characteristics in both. Methods: We conducted a retrospective cohort study of adult patients with histologically confirmed DHCS or CCS seen at The Ohio State University Comprehensive Cancer Center between 2010 and 2022. Demographics, treatment modalities, clinical outcomes, and molecular profiles were extracted and analyzed descriptively. Time to progression (TTP) and progression rates by treatment modality were recorded. A structured literature review was conducted to provide context for the findings. Results: Outcomes are descriptive and cohort-specific, reflecting institutional experience rather than generalizable estimates. A total of 10 patients with DHCS and 5 with CCS were evaluable. Most DHCS patients presented with metastatic disease. Among DHCS patients who received systemic therapies, 5 of 8 (62.5%) experienced progression during or shortly after treatment. Among CCS patients who received systemic therapies, 3 of 4 (75%) progressed during or shortly after treatment. Overall mortality occurred in 4 of 10 DHCS patients (40%) and 3 of 5 CCS patients (60%). TP53 mutations were identified in 4 of 7 next-generation sequencing (NGS)-tested DHCS cases, and PD-L1 positivity was detected in 5 of 7 tested DHCS cases and 1 of 5 tested CCS cases. Conclusions: Despite multimodal treatment, this referral-based cohort of patients with ultra-rare DHCS and CCS showed high rates of progression and mortality. Our findings underscore the urgent need for multi-institutional collaboration and biomarker-driven clinical trials to guide management of these ultra-rare sarcoma subtypes.