Alterations in cellular antigen processing and presenting machinery has gained increased interest as a hallmark of cancer-related inflammation. Growing evidence suggest that proteasome composition and immunoproteasome expression can influence antigen processing. By performing immunopeptidomics on A549 lung adenocarcinoma cell line following depletion of proteasome regulator PSME4 we identified alterations in the antigenic landscape resulting from changes in proteasome processing.