Anis Hamid, MBBS, Dana-Farber Cancer Institute, Boston, MA, discusses data from the phase I PRINCE trial (NCT03658447), which investigated 177Lu-PSMA-617 plus pembrolizumab for patients with metastatic castration resistant prostate cancer (mCRPC). Circulating tumour cells (CTCs) were found to correlate with patient outcomes, where levels of CTCs declined when patients had favorable outcomes 12 weeks after treatment. PSMA positron emission tomography (PET) metrics such as tumor volume were additionally associated with patient outcomes. This interview took place at the American Society of Clinical Oncology (ASCO) 2022 Annual Meeting in Chicago, IL.