LAUSR

Changes in serum prostate-specific antigen (PSA) levels, commonly used to evaluate the response of patients with metastatic castration-resistant prostate cancer to treatment, correlate poorly with overall survival. Circulating tumour cell (CTC) counts were explored as an end point in five prospective randomized phase III trials (total n = 6,081 patients). Among five CTC-based and three PSA-based end points, CTC0 (CTC count ≥1 at baseline and 0 at week 13) and CTC conversion (CTC count ≥5 at baseline and ≤4 at week 13) had the highest discriminatory power with respect to overall survival. In the trials analysed, CTC0 was reported for 75% of patients, but only 51% of these patients had CTC conversion. CTC0, a clinically meaningful end point that occurs shortly after treatment initiation, was deemed more reliable than PSA changes.