Molecular pathology of bladder cancer

Significant progress has been achieved in elucidating the molecular underpinnings of bladder cancer initiation and progression. Translational research has identified mutations in chromatin-modifying genes such as KMT2D and KDM6A, which facilitate colonization of larger regions of the urothelium. Subsequent mutations in TP53, PIK3CA, FGFR3 or RB1 drive malignant transformation. Advances in personalized oncology now integrate clinical, pathological and molecular classifications in bladder cancer, representing a paradigm shift in the management of locally advanced and metastatic disease. Alterations in FGFR3, commonly found in the luminal-papillary molecular subtype associated with low response to immunotherapy, are the target of erdafitinib. Enfortumab vedotin, which targets Nectin-4 (expressed in >95% of urothelial carcinomas), is approved for patients who progress after chemotherapy and/or immunotherapy. Evidence suggests that Nectin-4 gene amplification may further refine patient stratification. Sacituzumab govitecan, an antibody–drug conjugate directed against Trop-2, is effective in basal, luminal and stroma-rich subtypes but not in neuroendocrine carcinomas. In addition, therapies developed for HER2-positive breast cancer have shown efficacy in urothelial carcinoma, with recent data from the DESTINY pan-tumour phase II trial leading to FDA approval of trastuzumab deruxtecan for HER2-overexpressing metastatic urothelial carcinoma. This paper is a comprehensive review of the molecular pathology of bladder cancer, highlighting advances in molecular classification, biomarkers and personalized therapies. The transition from morphology-based classifications to combined morphological and molecular approaches, with therapeutic implications, is also addressed.