Introduction: Radiotherapy (RT) is the standard of care for over 50% of prostate cancer (PCa) patients, but up to 25% develop delayed bladder toxicities months to years after treatment. Late radiation cystitis is a dose-limiting toxicity that can cause hematuria and other potentially severe symptoms, leading to further morbidity and decisional regret. Additional work is needed to define early biomarkers of late radiation cystitis in order to better guide patient care. Extracellular vesicles (EVs) are stable membrane-enclosed particles that are released from diverse cell types and present at high levels in biofluid samples, but the relationship between EV biogenesis and the development of late radiation cystitis has not been examined. This study was developed to explore the relationships between late hematuria incidence and urinary and serum EV concentrations in a cohort of PCa patients undergoing RT. Methods: PCa patients scheduled to receive curative-intent external beam RT with or without brachytherapy boost were enrolled for this study. Longitudinal urine and serum samples were collected on enrollment (pre-treatment) and within 1 week after RT. Patients completed outcome questionnaires containing questions regarding radiation-related symptoms and quality of life at the time of sample collection, 6 months post-RT, and annually after RT for up to 5 years. Demographic, clinical, and treatment data were obtained from electronic medical records. EVs in collected urine and serum samples were quantified through a nanoparticle tracking analysis approach, and EV concentrations at different collection time points were then compared between patients that did and did not develop hematuria. Results: RT was found to significantly increase post-RT urinary EV concentrations relative to pre-RT levels in patients who subsequently developed late hematuria, whereas this induction of enhanced EV biogenesis was not observed in patients who did not develop this toxicity. The same effect was evident but less robust in patient serum samples. Re-examination of prior GWAS data additionally revealed that RT-related hematuria risk was strongly associated with the EV biogenesis-related genes SYTL3 and COG. Conclusions: Post-treatment EV concentrations in urine samples collected from PCa patients undergoing RT are associated with the future onset of radiation cystitis, providing a promising biomarker that may enable the more-timely treatment of at-risk patients to mitigate the development of late bladder toxicities. SOURCE OF Funding: University of Rochester departmental research funding.
