Background: Increased availability of treatment options in CRPC requires improved biomarkers to optimize decision making for therapeutic sequencing. Despite evidence for the value of CTCs in assessing prognosis and response to treatment, their use in clinical practice is not widely implemented. Clinicians rely on PCWG2 criteria based on PSA, clinical and radiological criteria although these are only inconsistently used in clinical practice. We evaluated the trends for clinical decision-making by physicians treating CRPC. Methods: An online questionnaire was distributed to physicians treating PC from the UK, Switzerland and Australia. Questions on clinical practice, familiarity with progression criteria, use of CTCs and clinical-decision making were formulated. Results: 111 participants replied. Most (84.7%) were oncologists treating ≥ 50 patients per year (65.3%). Although only 39.6% usually used PCWG2 in clinical practice, 74.5% considered PSA, bone scans and CT to be useful for monitoring disease. 55.6% considered PSA to be an important biomarker. A minority were able to identify PSA (41.4%) and bone scan (39.4%) progression criteria by PCWG2. On average, more physicians discontinued cabazitaxel (28%) than docetaxel (10.4%) before cycle 4. Similar number of cycles were given to bone only disease compared to RECIST evaluable patients. Clinical progression was most important for switching treatment for most physicians (90.5%), followed by RECIST (71.6%), bone scan (47.7%), CTC (23.2%) and PSA (21.1%). The main challenge associated with the use of CTCs was the access to technology (84.7%). Most respondents (92%) would not stop therapy with rising PSA but falling CTC counts; most (88.8%) would not stop with declining PSA but rising CTCs. Although 50% acknowledged the prognostic value of CTCs, only 33% would use them to guide decision-making. Conclusions: A significant number of physicians discontinue treatment before 12 weeks. Most physicians rely on clinical progression for decision-making. Knowledge of PCWG2 response and progression criteria is generally suboptimal. Greater physician awareness, access to technology and further evidence and will be required for the implementation of CTCs as a routine biomarker in CRPC.