Breelyn A. Wilky

Background: The publication of SARC028 in late 2017 revolutionized soft tissue sarcoma (STS) treatment by demonstrating promising response to anti‐PD1 immunotherapy in undifferentiated pleomorphic sarcoma (UPS) and dedifferentiated liposarcoma (DDLPS). Data on immunotherapy efficacy and outcomes in larger cohorts and with longer follow‐up remain limited. Methods: 31 672 cases of UPS, DDLPS, alveolar soft part sarcoma, and myxofibrosarcoma were extracted from the NCDB. Factors associated with the use of immunotherapy were evaluated using logistic regression, and survival analysis was performed with Kaplan‐Meier curves and Cox proportional hazards models. Results: Patients diagnosed with STS after 2017 were 3.67 times more likely to receive immunotherapy. Immunotherapy was associated with an approximately 20% reduction in mortality in stage IV STS, which was driven by cases of UPS. This survival benefit was observed in male, but not female, patients. There was no survival benefit in stage III STS. Discussion: These data are consistent with a survival benefit with immunotherapy in stage IV STS, predominantly in UPS, supporting the findings of SARC028. Benefit in stage III STS was not observed, limiting concordance with later trials like SARC032. Further prospective data on long‐term outcomes and immunotherapy efficacy according to histology and sex are needed.

Figure S1. Study design and treatment schedule

Generalizability to sarcoma population

Complete clinical and genetic details of patients

Figure S2. Representative cross-sectional imaging for selected responding patients.

Figure S3. Post-hoc analysis comparing stage 1 and stage 2 clinical outcomes.

Serum cytokines from Luminex analysis not included in the main figures and cytokine levels in tumor interstitial fluid

Flow gating strategy and TIL phenotypes not included in the main figures