Immunoprofiling in alveolar soft part sarcoma.

11059Background: Alveolar Soft Part Sarcoma (ASPS) is a distinctive tumor characterized by a canonical ASPL-TFE3 fusion. Treatment options are limited. We assessed tumor immune cell infiltrates, and correlated this with patients receiving PD-1 blockade. Methods: A retrospective institutional review was performed for 18 cases of ASPS. Immunohistochemistry was performed on paraffin-embedded tissue (PET) for T-lymphocyte markers (CD3/CD4/CD8), and PD-1/PD-L1 (Ventana). Expression was quantified by standard methods: (total cells per high power field: score; 0:0; 1-10:1; 11-50:2; 50-99:3; 100:4). Select cases underwent DNA sequencing analysis using whole exome (WES, > 80X, n = 4) and genome (WGS, > 30X, n = 1) sequencing. Indel analysis was conducted via mutect2 ( > 5% variant allele frequency) and mutational signature was performed using deconstructSigs. Results: The median age was 27 (15-54). Disease status at diagnosis was: 44% localized; 56% metastatic. The median overall survival was 17 yrs (2.9-31). Four...