Molecular carcinogenesis of urinary bladder cancer

Since the 1970s, research on molecular carcinogenesis of urinary bladder cancer (UBC) has concentrated on the dual-track mode, which describes the genesis of papillary tumors on the one hand and invasive, non-papillary carcinomas on the other hand [1, 2]. This model was for a long term the basic meshwork of molecular UBC categorization and research design. Sjödahl et al. [3] recently proposed a novel approach describing a molecular taxonomy for bladder cancer based on gene expression profiling data obtained from tumors of all grades and stages. This milestone work introduced five new categories into which UBC cases can be divided. Based on these insights, it was possible to catch up with other tumor entities, behind which the knowledge about molecular carcinogenesis in UBC was lacking for a long time. This chapter introduces the classic dual-track model of papillary versus non-papillary urinary bladder carcinogenesis followed by the molecular taxonomy developed in the last few years, highlighting the five novel subcategories of UBC introduced recently: urobasal A (UroA), UroB, genomically unstable (GU), squamous cell carcinoma-like (SCCL), and "infiltrated".