Atezolizumab (PD-L1) Delivers 37-Month DoR in ASPS, with Fusion Subtype Driving Benefit

Atezolizumab (Tecentriq), an anti–PD-L1 monoclonal antibody, was given to patients with unresectable/metastatic alveolar soft part sarcoma (ASPS) in the pivotal single-arm Phase II Study ML39345 (NCT03141684; n=53) with ~3 additional years of follow-up. ORR remained 35.8% (95% CI, 23.1-50.2) with mPFS 20.8 months (IQR, 7.6–NR), while median duration of response deepened to 37.0 months; by comparison, VEGFR TKI benchmarks in ASPS (e.g., cediranib) have reported ORR ~19-35% with mPFS ~10 months, typically without multi-year immunotherapy-style durability. Fusion subtype looked predictive: among 47 genotyped patients, type 1 ASPSCR1::TFE3 had higher ORR 43.9% and mPFS 28.3 months vs type 2 with ORR 0% and mPFS 7.5 months (PFS HR 3.2, 95% CI, 1.01-10.2); an on-protocol “drug holiday” after ≥2 years (n=11; 3.5-26.4 months) saw progression in 2 patients, and bevacizumab+atezolizumab post–mono-progression (n=9) produced ORR 0% with mPFS 18.5 months (IQR, 7.9-21.1).