Clinical, immunological, and genomic findings of atezolizumab in advanced alveolar soft part sarcoma: A phase II trial (ALBERT trial/NCCH1907)

Purpose Alveolar soft part sarcoma (ASPS) is a rare subtype of soft tissue sarcoma with a high metastatic potential. We conducted a phase II clinical study of atezolizumab in ASPS patients to evaluate its efficacy, safety, and biomarkers associated with therapeutic response. Patients and Methods Eligible patients were aged ≥16 years and diagnosed with ASPS. Atezolizumab was administered at a dose of 1200 mg every 3 weeks. The primary endpoint was the objective response rate (ORR). Immune and genomic profiling of tissues was performed using immunohistochemistry, RNA sequencing, and whole-exome sequencing. Results Twenty patients were included in the study. The median age was 32.5 years, and 12 patients (60%) received pazopanib. The overall ORR was 10% (2 of 20). Two patients (10%) achieved a complete response, which persisted for more than 1 year. Fourteen patients (70%) had stable disease. The disease control rate was 80%. Responders exhibited abundant infiltration of CD8 + PD-1 + T cells, characterised by low expression of Tim-3 and LAG-3. Conclusion Atezolizumab was effective in some patients, regardless of prior treatment with pazopanib. Responders had significant PD-1 expressing CD8 + T cell infiltration before immune checkpoint inhibitor therapy. The degree of CD8 + PD1 + T cells may be a potential biomarker for predicting responses to atezolizumab.