Circulating Tumor DNA in Urothelial Cancer: Practical Applications in Oncology Clinic.

Circulating tumor DNA (ctDNA) is increasingly being used to monitor minimal residual disease (MRD) in various solid tumors, including urothelial carcinoma (UC). It has emerged as a promising biomarker for MRD and may serve as a valuable tool to guide treatment decisions, particularly in patients at high risk of recurrence after definitive therapy or those experiencing favorable responses to systemic therapy in the setting of locally advanced or metastatic disease. ctDNA technology is largely agnostic to the type of tumor, which can be either hematologic or solid organ malignancies. Its clinical utility requires validation across different tumor types as ctDNA release kinetics and threshold values for testing often vary. Moreover, it is essential to evaluate ctDNA testing across a range of clinical scenarios, including screening, diagnosis, prognosis, and therapeutic decision making. The optimal frequency and duration of testing also need to be defined, particularly in settings such as postdefinitive therapy and ongoing chemotherapy for metastatic disease. In this study, we will summarize the current literature on the role of ctDNA in urothelial cancer. We will discuss the data that inform us of current clinical practice. Furthermore, we will explore evolving developments in the field from other tumor types and potential future directions in UC. Finally, we will highlight selected clinical scenarios for applications of ctDNA testing and its interpretation.