Molecular Subtypes of Bladder Cancer

Recent whole genome characterizations of primary human bladder cancers revealed that they can be grouped into "intrinsic" basal and luminal molecular subtypes. Here, we provide an overview of the subtypes and discuss their biological and clinical properties. Basal cancers are characterized by advanced stage and metastatic disease at presentation. They tend to be enriched with squamous and small cell/neuroendocrine features and inactivating mutations and deletions of TP53 and RB1. Basal cancers can be divided into "epithelial" and "mesenchymal" (also known as "claudin low") subsets, and a portion of the latter form a "neuroendocrine/neuronal" subset that is associated with particularly poor survival. Luminal cancers are often enriched with papillary histopathological features and activating mutations in FGFR3, and they can also be divided into additional subsets based on differential stromal cell infiltration, relative genomic instability, and high- versus low-level expression of carcinoma in situ (CIS) gene expression signatures. Importantly, the bladder cancer molecular subtypes display differential sensitivities to neoadjuvant chemotherapy and immune checkpoint blockade, and preliminary data also suggest that they respond differently to radiation with or without hypoxia modulation. Ongoing studies are investigating the relevance of the molecular subtypes to the bladder cancer histopathological variants and to upper tract urothelial cancer. The bladder cancer molecular subtypes were associated with different prognoses and responses to conventional and targeted therapies in retrospective studies. If validated in prospective studies, molecular subtyping will be integrated into bladder cancer clinical management.