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Background: In ultra-rare sarcomas (URS) the conduction of prospective, randomized trials is challenging. Data from retrospective observational studies (ROS) may represent the best evidence available. ROS implicit limitations led to poor acceptance by the scientific community and regulatory authorities. In this context, an expert panel from the Connective Tissue Oncology Society (CTOS), agreed on the need to establish a set of minimum requirements for conducting high-quality ROS on the activity of systemic therapies in URS. Methods: Representatives from > 25 worldwide sarcoma reference centres met in November 2020 and identified a list of topics summarizing the main issues encountered in ROS on URS. An online survey on these topics was distributed to the panel; results were summarized by descriptive statistics and discussed during a second meeting (November 2021). Results: Topics identified by the panel included the use of ROS results as external control data, the criteria for contributing centers selection, modalities for ensuring a correct pathological diagnosis and radiologic assessment, consistency of surveillance policies across centers, study end-points, risk of data duplication, results publication. Based on the answers to the survey (55 of 62 invited experts) and discussion the panel agreed on 18 statements summarizing principles of recommended practice. Conclusions: These recommendations will be disseminated by CTOS across the sarcoma community and incorporated in future ROS on URS, to maximize their quality and favor their use as control data when results from prospective studies are unavailable. These recommendations could help the optimal conduction of ROS also in other rare tumors.

BACKGROUND: No prospective trial with anthracycline-based chemotherapy has individually assessed response in a well-differentiated (WD)/dedifferentiated (DD) liposarcoma patient cohort. We conducted a retrospective analysis of first-line chemotherapy in liposarcoma of intra-abdominal origin (IA-LPS) in patients who had entered the European Organisation for Research and Treatment of Cancer (EORTC)/Soft Tissue and Bone Sarcoma Group (STBSG) trials. METHODS: We searched for all adult patients treated with first-line chemotherapy for advanced IA-LPS in the EORTC STBSG phase 2 and 3 trials from 1978. Treatment was aggregated into 5 groups: anthracycline alone, ifosfamide alone, doxorubicin plus ifosfamide (D+IFO), doxorubicin/cyclophosphamide/vincristine/dacarbazine, and “other” (brostallicin, trabectedin). Response was assessed prospectively by Response Evaluation Criteria in Solid Tumors or World Health Organization criteria. Progression-free survival (PFS) and overall survival (OS) were computed by Kaplan-Meier method. RESULTS: A total of 109 patients with IA-LPS from 13 trials were identified (104 evaluable for response). Overall, there were 10/109 (9.2%) responders: 3/48 (6.3%) in the anthracycline alone group, 2/15 (13%) in the ifosfamide alone group, and 4/18 (22%) in the D+IFO group. At the 10-month median follow-up (interquartile range, 6-24), the median OS was 19 months (95% CI, 15-21) and median PFS 4 months (95% CI, 3-6). D+IFO achieved a not statistically significant longer median PFS (12 months) and median OS (31 months) than observed with other regimens. Univariate/multivariate analysis did not identify prognostic factors. CONCLUSIONS: Cytotoxic chemotherapy, in particular anthracycline alone, had marginal activity in advanced IA-LPS. Ifosfamide-containing regimens showed higher activity, although it was not statistically significant and in a small number of cases, with the combination of doxorubicin and ifosfamide appearing to be the more active regimen available in fit patients. This series provides a benchmark for future trials on new drugs in WD/DD liposarcoma.;.