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Background: Mesenchymal chondrosarcoma (MCS) is an ultra‐rare sarcoma that follows a more aggressive course than conventional chondrosarcoma. This study evaluates prognostic factors, treatments (surgery, chemotherapy, and radiation), and outcomes in an Australian setting. Methods: We collected demographics, clinicopathological variables, treatment characteristics, and survival status from patients with MCS registered on the national ACCORD sarcoma database. Outcomes include overall survival (OS) and progression‐free survival (PFS). Results: We identified 22 patients with MCS between 2001–2022. Median age was 28 (range 10–59) years, 19 (86%) had localised disease at diagnosis of whom 16 had surgery (84%), 11 received radiation (58%), and 10 chemotherapy (53%). Ten (52%) developed recurrence and/or metastases on follow‐up and three patients with initial metastatic disease received surgery, radiation, and chemotherapy. At a median follow‐up of 50.9 (range 0.4–210) months nine patients had died. The median OS was 104.1 months (95% CI 25.8–182.3). There was improved OS for patients with localised disease who had surgical resection of the primary (p = 0.003) and those with ECOG 0–1 compared to 2–3 (p = 0.023) on univariate analysis. Conclusions: This study demonstrates contemporary Australian treatment patterns of MCS. The role of chemotherapy for localised disease remains uncertain. Understanding treatment patterns and outcomes help support treatment decisions and design of trials for novel therapeutic strategies. [ABSTRACT FROM AUTHOR]

CIC‐rearranged sarcoma is a recently established, ultra‐rare, molecularly defined sarcoma subtype. We aimed to further characterise clinical features of CIC‐rearranged sarcomas and explore clinical management including systemic treatments and outcomes. Methods: A multi‐centre retrospective cohort study of patients diagnosed between 2014–2019. Results: Eighteen patients were identified. The median age was 27 years (range 13–56), 10 patients were male (56%), 11 patients (61%) had localised disease and 7 patients had advanced (metastatic or unresectable) disease at diagnosis. Of 11 patients with localised disease at diagnosis, median overall survival (OS) was 40.6 months and the 1‐, 2‐ and 5‐year OS estimates were 82%, 64% and 34% respectively. Nine patients (82%) underwent surgery (all had R0 resections), 8 (73%) patients received radiotherapy to the primary site (median dose 57Gy in 28 fractions), and 8 (73%) patients received chemotherapy (predominantly Ewing‐based regimens). Metastases developed in 55% with a median time to recurrence of 10.5 months. In patients with advanced disease at diagnosis, median OS was 12.6 months (95% CI 5.1–20.1), 1‐year OS was 57%. Median progression‐free survival was 5.8 months (95% CI 4.5–7.2). Durable systemic therapy responses occurred infrequently with a median duration of systemic treatment response of 2.1 months. One durable complete response of metastatic disease to VDC/IE chemotherapy was seen. Responses to pazopanib (n = 1) and pembrolizumab (n = 1) were not seen. Conclusion: In this series, CIC‐rearranged sarcomas affected young adults and had a high incidence of presenting with, or developing, metastatic disease. The prognosis overall was poor. In advanced disease, durable systemic therapy responses were infrequent. [ABSTRACT FROM AUTHOR]