Response to Immune Checkpoint Inhibition in Two Patients with Alveolar Soft Part Sarcoma

Alveolar soft-part sarcoma (ASPS) is a morphologically distinctive mesenchymal tumor characterized by a canonical ASPL–TFE3 fusion product. In the metastatic setting, standard cytotoxic chemotherapies are typically ineffective. Studies have suggested modest clinical response to multitargeted receptor tyrosine kinase inhibitors. Here, we report sustained partial responses in two patients with immune checkpoint inhibition treated with either durvalumab (anti–PD-L1) alone or in combination with tremelimumab (anti–CTLA-4), which appeared unrelated to tumor immune infiltrates or mutational burden. Genomic analysis of these patients, and other cases of ASPS, demonstrated molecular mismatch-repair deficiency signatures. These findings suggest that immune checkpoint blockade may be a useful therapeutic strategy for ASPS. Cancer Immunol Res; 6(9); 1001–7. ©2018 AACR .