A recent study suggests that circulating tumor cell count as a response measure of prolonged survival may be a meaningful endpoint for early-phase metastatic castration-resistant prostate cancer.
As the treatment landscape continues to evolve for patients with metastatic castration-resistant prostate cancer, the need for more reliable endpoints to evaluate the benefit of clinical interventions is also growing.
Glenn Heller, MD, Memorial Sloan Kettering Cancer Center (New York, NY), and colleagues conducted a study to assess circulating tumor cell and prostate-specific antigen (PSA) response endpoints in phase III studies involving patients with metastatic castration-resistant prostate cancer. A total of five prospective randomized phase trials (COU-AA-301, AFFIRM, ELM-PC5, ELM-PC4, and COMET-1) enrolling 6081 patients were analyzed for the study.
Eight circulating tumor cell and PSA response measures were investigated – circulating tumor cell count of at least 1 at baseline and 0 at week 13 (CTC0); patients with a count of 5 or higher at baseline and 4 or fewer at week 13 (CTCconv); circulating tumor cell counts of 5 or greater at baseline and a 30%, 50%, or 70% decline from baseline to week 13, respectively; and PSA level 5 ng/mL or greater at baseline and a 30%, 50%, or 70% decline from baseline to week 13, respectively.
Researchers used weighted c-indices—ranging from 0.5 to 1.0—with a higher index representing a greater likelihood of longer survival for patients who responded to treatment.
Results of the study were published in the Journal of Clinical Oncology (online December 22, 2017; doi:10.1200/JCO.2017.75.2998).
Among the eight response endpoints, researchers reported that CTC0 and CTCconv were the most useful markers for differentiating survival outcomes between patients who responded and those who did not respond to therapy at week 13. The average weighted c-indices for CTC0 and CTCconv were 0.81 and 0.79, respectively.
Dr Heller and colleagues concluded that “both CTC0 and CTCconv are robust and meaningful response endpoints for early-phase metastatic castration-resistant prostate cancer clinical trials.”—Zachary Bessette