(UroToday.com) The European Society of Medical Oncology (ESMO) 2021 virtual annual meeting’s prostate cancer session included a presentation by Dr. Johann de Bono presenting data assessing the impact of circulating tumor cell (CTC) morphologic sub-types prior to treatment in the CARD trial.1 In the CARD study (NCT02485691), cabazitaxel significantly improved radiographic progression-free survival (rPFS) and overall survival (OS) versus abiraterone or enzalutamide in patients with metastatic castration-resistant prostate cancer who had received docetaxel and progressed ≤ 12 months with the alternative androgen receptor-targeted agent. There is a current unmet need to identify superior monitoring tools of treatment efficacy so that patients do not remain on ineffective therapies when they no longer clinically benefit from them. CTC counts are a validated pretreatment prognostic measure, as well as a validated tool for response monitoring. The objective of this pre-planned CARD EPIC biomarker study was to analyze the morphology of CTC subtypes in a liquid biopsy.