Heitzeneder S, et al. - Researchers focused on the biological roles for pregnancy-associated plasma protein A (PAPP-A) in Ewing sarcoma (EWS) in vitro and in vivo in NSG xenograft models as well as carried out RNA-sequencing on PAPPA knockout clones (n = 5) and controls (n = 3). They investigated highly differentially expressed molecules via a comprehensive characterization of the surfaceome of EWS by comparing RNA expression of cell surface proteins in EWS (n = 120) vs normal tissues (n = 42). Eleven highly differentially overexpressed genes were identified in EWS surfaceome analysis, with PAPPA ranking second in differential expression. Via regulating local insulinlike growth factor (IGF)-1 bioavailability, an essential survival role was demonstrated in EWS cell lines by genetic knockout of PAPPA and treatment with anti-PAPP-A antibodies. EWS growth in orthotopic xenografts was diminished by MAb-mediated PAPPA inhibition, which also improved the efficacy of anti-IGF-1R treatment. Induction of interferon (IFN)-response genes, including proteins associated with antigen processing/presentation, was seen as a result of PAPPA knockout in EWS cell lines. In PAPPA-low EWS tumors, gene expression profiles were enriched for immune response pathways.