Chromosomal deletions in bladder cancer: shutting down pathways

Bladder cancer is one of the most common cancers in the world, leading to approximately 145,000 deaths annually. Bladder cancer is typically managed by surgical removal of the tumor; however, the recurrence rate is disappointingly very high, often requiring systemic chemotherapy. Improvement in the diagnosis and prognosis of bladder cancer will only come from a comprehensive understanding of the genetic factors that lead to its development. In this review, we focus on the chromosomal deletions that contribute to the downregulation of tumor suppressor pathways in bladder cancer. Chromosomal deletions are not a random event, since bladder cancer progression has been associated with specific chromosomal deletions and this progression correlates with specific stages of tumor development. The most commonly found chromosomal deletion in all stages of bladder cancer involves deletions in chromosome 9, resulting in the loss of three genes encoding proteins that activate the Rb and p53 tumor suppressors. Additionally, chromosome 9 harbors the TSC1 tumor suppressor which downregulates the well-known anti-apoptotic Akt/mTOR pathway. Hence, deletions on one chromosome may have a crucial influence on the initial steps in tumor development. Other deletions targeting the tumor suppressors Rb, p53, FHIT and LZTS1 occur at later stages of tumor development. Considering the central importance of these tumor suppressor pathways in the formation and evolution of tumors, the time has come to evaluate available drugs in bladder cancer that target the positive regulators of these pathways.