Bladder cancer: novel molecular characteristics, diagnostic, and therapeutic implications

Bladder cancer (BC) comes in two flavors: as non-muscle invasive (NMI) and as muscle invasive (MI) disease. These two subtypes differ in their genetic aberrations. In NMI-BC mutations in the FGFR3 oncogene are found with a frequency of 75%, whereas mutations in the TP53 tumor suppressor gene prevail in MI-BC. Mutations in the RAS genes occur in 15% of BC of all stages and are mutually exclusive with FGFR3 mutations. Mutations in the PIK3CA gene are found in about 13% and these almost exclusively co-occur with FGFR3 mutations. NMI-BC with FGFR3 mutations are genetically stable, but FGFR3 wild type NMI-BC and MI tumors are genetically unstable. In this paper, we discuss the use of these genetic aberrations in relation to recurrence, progression, surveillance, and therapeutic options. As of yet, there is no biomarker that can predict recurrences or the rate of recurrences when they occur. We show that FGFR3 mutations are associated with a decreased risk of progression, and a better survival both in BC and in upper urinary tract cancer. Microsatellite analysis (MA) in order to detect loss-of-heterozygosity can be used to detect recurrences in urinary cells of patients under surveillance. The results of a Dutch randomized trial show that consecutive positive MA results are a strong predictor for future recurrences. Using FGFR3 mutation analysis for those patients who have an FGFR3 mutant tumor will enhance performance of urine-based surveillance. Although FGFR3 mutations occur in only 20% of MI tumors, these tumors often have a high expression of the FGFR3 protein. This suggests that this receptor could present a target for adjuvant therapy in MI-BC. However, whether the FGFR3 pathway is active in these tumors remains to be established.