Pleomorphic rhabdomyosarcoma, outcomes of patients with advanced disease treated with systemic agents: Retrospective study from the global pushing ultra-rare sarcomas towards hope (PUSH) consortium

OBJECTIVES: To report the outcomes in adult patients with advanced pleomorphic rhabdomyosarcoma (P-RMS) treated with systemic therapy. METHODS: This global, multicenter, retrospective study conducted within the Pushing Ultra-Rare Sarcomas Towards Hope consortium (PUSH) included patients > 40 years with histologically confirmed advanced P-RMS, treated with at least one line of systemic therapy between 2013 and 2023. The primary endpoint was progression-free survival from first diagnosis of advanced disease, and from systemic treatment start (PFS-1 and PFS-2). Secondary endpoints included overall response rate (ORR), overall survival from first diagnosis of advanced disease and from treatment start (OS-1 and OS-2), and treatment-specific outcomes. RESULTS: Seventy-seven patients were included from 21 sarcoma reference centers. At a median follow-up of 44 months (IQR: 17.0-74.8), 49 (64%) patients had died and 48 (62%) had progressed. The median OS-1 and PFS-1 were 13.6 (95% confidence interval (CI): 9.4-22.5) and 5.4 (95% CI: 4.2-7.3) months, respectively. Two- and three-year OS-1 were 32.5% and 30.3%. Anthracycline-based regimens (n = 42) achieved a 50% ORR, with mPFS-2 and mOS-2 of 5.2 and 19.2 months; gemcitabine-based regimens (n = 15) a 42% ORR, with mPFS-2 and mOS-2 of 3.7 and 7.8 months; pazopanib (n = 6) a 33% ORR, with mPFS-2 and mOS-2 of 2.4 and 4.2 months; PD-1 inhibitors (n = 2) induced one response lasting 53 months. CONCLUSIONS: This series of advanced P-RMS treated with systemic agents, the largest available to date, showed meaningful activity of anthracycline- and gemcitabine-based regimens, and anecdotal responses to pazopanib and PD-1 inhibitors. Further prospective validation is planned.