Clinical benefit and fragility evaluation of systemic therapy trials for advanced soft tissue sarcoma

The clinical benefit of systemic anticancer therapies can be unclear despite positive trials, and outcomes may not translate to real-world practice. This study evaluated the benefit of soft tissue sarcoma (STS) treatments using the European Society of Medical Oncology Magnitude of Clinical Benefit Scale (MCBS) v1.1 and measured the robustness of STS trial results using Fragility Index (FI).

Database searches for adult phase II or III trials in advanced STS (January 1998-December 2023) were performed. Therapies with trial outcomes that met the criteria for MCBS were scored 1-5 (≥4 represents substantial clinical benefit). For randomized clinical trials with positive time-to-event endpoints, the number of additional events that would render results nonsignificant, FI, was calculated and expressed as a proportion of the experimental arm size (fragility quotient [FQ]). Higher FI/FQ implies more robust results.

Among 194 trials, 19 (9.8%) were phase III. Most phase II trials (146/175; 83.4%) had single-arm or non-comparative design. Trials that were eligible for MCBS scoring (n = 78; 40.2%) evaluated 56 different agents/regimens. Median MCBS score was 2. Only three agents/regimens (all cytotoxic therapies) had an MCBS score ≥4. Among 47 randomized clinical trials, 16 (8 phase II; 8 phase III) trials had positive outcomes. Median FI was 7 (range, 2-52) and 10 trials (62.5%) had an FQ < 10%, with median of 7% (range, 1%-59%).

Most systemic therapies in STS trials did not confer substantial clinical benefit per European Society of Medical Oncology-MCBS. Additionally, positive randomized trials were often fragile. Novel STS therapy trials should use clinically meaningful endpoints and real-world efficacy confirmation is essential, especially for less robust trials.