More prostate cancers are now detected at an early stage, largely due to the PSA test. While some cancers are slow-growing and unlikely to threaten a man’s life, others are aggressive and require immediate treatment. Unfortunately, we currently lack reliable tools to tell us which course a tumour will take, resulting in unnecessary ‘over-treatment’ of men with non-threatening cancer, and missed or delayed treatment of aggressive disease. An exciting recent discovery is that cancer cells release small packages of information, called extracellular vesicles (EVs), into body fluids such as urine. EVs contain an enriched source of ‘red flags’ for disease, called biomarkers. We aim to isolate EVs from patient urines, using a rapid and efficient method we developed, and profile their number and contents to identify and improve upon biomarkers indicative of prostate cancer aggressiveness. Such EV biomarkers could help physicians and patients more confidently make appropriate treatment decisions