Dendritic/histiocytic cell sarcoma: The OSU experience

e23552 Background: Dendritic and histiocytic cell sarcomas (DHCS) are ultra-rare malignant neoplasms with morphological and immunotypic features of histiocytes. Incidence rates are unknown, it is estimated to represent < 1% of all soft tissue tumors. Diagnosis is often challenging due to histological variability and lack of a pathognomonic molecular marking. Currently, there is no well-defined standard of care for these patients. This study describes a single-center experience with and this is one of the largest cohorts reported in the medical literature. Methods: Patients evaluated at The Ohio State University James Comprehensive Cancer Center between January 1, 2010 and April 1, 2022, were included. Data collected included baseline demographic variables, pathologic and molecular features, treatment regimen, and outcomes. Due to a small cohort size, descriptive statistics were performed instead of formal power calculations. Results: 18 patients were identified. 8 were censored, as they did not receive treatment at our institution, or were lost to follow-up, out of the 10 evaluable patients. Nine (90%) were white, and 7 (70%) were male. The median age at diagnosis was 54 years (24-67). The most common anatomic location was the head and neck region (60%). The average size of the tumor was 4.8 cm. 4 out of 10 patients presented with localized disease, and 6 with metastatic disease. 8 patients received chemotherapy, 3 received radiation therapy, and 3 patients underwent surgery. The patients who received chemotherapy underwent a range of 2 to 6 cycles, utilizing a variety of regimens, most commonly cytotoxic chemotherapies. We analyzed the time to progression (TTP) for each line of treatment for each patient the shortest TTP for a chemotherapy line was 16 days for a patient who received single-agent Sirolimus. A patient who received Cyclophosphamide, Doxorubicin, and Vincristine had the longest TTP at 354 days (or 51 weeks). Due to the small sample size, progression rates were calculated instead of median TTP. Five of the 8 patients that received chemotherapy progressed (62.5%), while a third progressed (33.3%) if they had received radiation or surgery. Four of the 10 patients (40%) died from the disease within the dates studied. 7 of 18 patients underwent somatic NGS testing. 4 of the 18 had a TP53 mutation, and 5 of the 7 patients who received NGS testing had a positive PD-L1 expression level. The median tumor mutation burden was 4.75(3-127). Conclusions: We found that DHCS a has relatively unfavorable outcomes despite aggressive multi-modality treatment. Due to the limited sample size, we could not identify significant associations between clinicopathological factors and treatment outcomes. However, the descriptive data suggests multidisciplinary approach may lead to better outcomes. We recommend multi-institutional collaboration to design clinical trials and define optimal treatment strategies for patients with this ultra-rare sarcoma.