PYGB and inverted urothelial papilloma: In the current study, we applied in-depth proteomics-based machine learning analysis and presented two novel findings as follows: 1) the comprehensive proteomic landscape of IUP to stratify its oncologic risk by identifying two subgroups, a low-risk and a high-risk and 2) a novel immunohistochemical biomarker PYGB to differentiate IUP from PUC with inverted growth.