(P 343) PROGRESSION FREE SURVIVAL OF IMMUNE CHECKPOINT INHIBITORS IN THE FIRST-LINE TREATMENT OF METASTATIC SARCOMA: A SINGLE CENTER RETROSPECTIVE ANALYSIS.

Objective: The role of immune checkpoint inhibitors (ICI) in the treatment of metastatic sarcoma remains off-label or investigational. Sarcomas are largely chemotherapy resistant, and there is an urgent need to explore alternative treatments in sarcoma to prolong survival.

Methods: Patients with metastatic sarcoma who received first-line ICI at our institution were identified via electronic medical records for retrospective analysis from May 2012 to July 2024. Patient (pts) and disease characteristics, including histology, PD-L1 tumor proportion score (TPS), and metastatic sites, were analyzed. PFS (date of metastasis diagnosis to disease progression or death due to any cause) was estimated using the Kaplan-Meier method, and Cox regression was used to assess the significance of covariates on PFS.

Results: Cohort had 94 patients with median age 63 years, 51% male, 49% undifferentiated sarcoma, 18% leiomyosarcoma, 31% other sarcomas. With regards to metastases, 63% had lung, 14% liver, and 15% bone. Of 94 patients, 61 patients had PD-L1 staining available. TPS were 0 for 46%, 1 for 3%, and 2 and 3 for 25% each. 94% received pembrolizumab, 4% Nivolumab (3 with ipilimumab and 1 with relatlimab), and the remainder had trial enrolment.  ICI monotherapy was employed in 85%, and in combination with other systemic treatments in 15%. Median PFS for all patients was 16.7 months. By histology, median PFS was 35.6 months for leiomyosarcoma, 9.2 months for undifferentiated sarcoma, and 18.5 months for other sarcomas. Patients receiving monotherapy had a median PFS of 17.5 months, compared to 15 months for combination therapy. The 6- months, 1-, 2-, 3-, 4-, and 5-year PFS rates were 76%, 57%, 37%, 23%, 19%, and 15% respectively. The 3-year PFS rate for leiomyosarcoma was higher numerically than undifferentiated sarcoma (39% versus 23%), thereafter did not show any difference in survival. No patient or disease characteristics, including TPS, histology, or metastatic sites, were significantly associated with PFS.

Conclusion: We present a real-world retrospective study in patients with sarcoma treated with first- line checkpoint inhibitor immunotherapy. The PFS was encouraging at 16.7 months, with an intriguing revelation of better survival in leiomyosarcoma numerically. Our results could be biased due to patient selection, but it remains an area of study that should be promoted. Further studies should prospectively assess PFS in sarcoma in the first- line setting, given poor outcomes with chemotherapy.