Using the neoadjuvant chemotherapy paradigm to develop precision therapy for muscle-invasive bladder cancer

• The neoadjuvant chemotherapy paradigm is attractive for biomarker and drug discovery
• Abundant tissue before and after chemotherapy enables detailed molecular analysis
• Immediate readouts include pathologic response and pharmacodynamics measures
• Drug testing in patient derived xenografts is used to predict patient response.
• Analysis of cell-free DNA enables assessment of evolving tumor molecular environment

BackgroundBladder cancer is a leading cause of morbidity and mortality. Despite recent advances in understanding its molecular biology, the 5-year survival for muscle-invasive disease (muscle-invasive bladder cancer [MIBC]) remains approximately 50%. Although neoadjuvant chemotherapy (NAC) offers an established 5% absolute survival benefit at 5 years, only the 40% of patients with a major tumor response appear to benefit. There remains, therefore, a critical unmet need for predictive markers to determine which patients are best managed with NAC, as well as for novel targeted therapies to overcome resistance to NAC.MethodsThe NAC paradigm offers the optimal clinical context for developing precision therapy for MIBC. Abundant tissue is available for analysis before NAC in all patients and after NAC in patients with residual MIBC. Technologic advances have enabled next-generation sequencing and gene expression microarray analysis of routinely collected and even archived tissue specimens. These technologies provide a foundation for the identification of markers of chemoresistance and for the development of rational cotargeting strategies.ResultsModern computational methods allow for some measure of target validation, which can be enhanced by the use of patient-derived primary xenografts (PDX). These PDX can be established at the time of radical cystectomy after NAC if there is residual MIBC. By the time a patient recurs clinically, candidate drugs targeting specific molecular changes in the patient tumor and corresponding PDX would have been tested in the PDX model, and only the most efficacious drug(s) would be administered to the patient. Liquid biopsies in the form of circulating tumor DNA and circulating tumor cells allow noninvasive longitudinal monitoring of the molecular landscape of an advanced tumor as it is being treated with successive courses of systemic therapy.ConclusionsThese tools combined form the foundation of an evidence-based precision oncology strategy for MIBC.