CTC Cells Predictors of Survival in Men Treated with Abiraterone Acetate

San Diego—Among patients with metastatic castration resistant prostate cancer (mCRPC), circulating tumor cells (CTCs) are established biomarkers to predict response to chemotherapy. A recent biomarker panel comprising CTC has also demonstrated predictive value for survival in men treated with abiraterone acetate following chemotherapy in the COU-AA-301 pivotal trial.

Researchers led by Christian Meyer, MD, presented long-term data of a sub-analysis of the German named patient program (nPP) at the AUA 2016 Annual Meeting in a session titled Long-Term Follow-Up of Circulating Tumor Cells as Predictors for Survival in Men Treated with Abiraterone Acetate for Castration Resistant Prostate Cancer following Chemotherapy.

In the context of the national nPP prior to the approval of abiraterone acetate in Europe, the data included 37 patients with mCRPC who progressed following at least one but not more than two prior chemotherapy regimens, including cyclophosphamide (CTX). Treatment comprised 100 mg of abiraterone acetate daily plus 5 mg prednisone twice a day until disease progression or unacceptable toxicity.

A full blood cell save tube was drawn at baseline. CTC evaluation was done according to the Cell Search Epithelial Cell Test protocol (Veridex, Raritan, New Jersey). On each monthly follow-up visit, subsequent CTC measurements were performed. The influence of independent predictors on overall survival was assessed using Kaplan-Meier estimates and Cox regression analysis.

Compared with the patients in COU-AA-301, the study cohort in this analysis was older (71.3 years), had a higher median PAS (297 ng/mL), and lower proportions of significant pain (20%) and visceral metastasis (8%). Following a median follow-up of 17.7 months, 35 of 37 patients died. Of the 37 men, 50% showed a decrease in PSA of ~30% and 38% showed a PSA decrease of ~50%.

Unadjusted Kaplan-Meier estimates demonstrated a significant survival benefit for patients with CTC counts <5 versus any CTC converters (P<.001). In univariable Cox regression models, independent predictors of overall survival were baseline PSA, hemoglobin, time under abiraterone acetate, the number of systemic therapies following discontinuation of abiraterone acetate, and CTC converters. Time of treatment under abiraterone acetate and the number of subsequent treatment lines after abiraterone acetate remained independent predictors of overall survival in multivariable Cox proportional hazard models: hazard ratio [HR], 0.87; 95% confidence interval [CI], 0.81-0.95; P=.001 and HR, 0.33; 95% CI, 0.11-0.97; P=.04, respectively).

In summary, the researchers said, “In our long-term analysis of the German named patient program with the primary end point met by 35/37 patients, we confirmed the role of CTC enumeration as an early indicator of treatment response. Although CTC counts failed to have significant association with overall survival in a multivariate context, it early indicates response to abiraterone acetate in men pretreated with CTX. In addition, our study underlines the importance of access to subsequent therapies with proven survival benefit for men with mCRPC after CTX and abiraterone acetate.”

Source: Meyer C, Strölin P, Heinzer H, Pantel K, Riethdorf S, Steuber T. Long-term follow-up of circulating tumor cells as predictors for survival in men treated with abiraterone acetate for castration resistant prostate cancer following chemotherapy. Abstract of a presentation at the American Urological Association 2016 Annual Meeting, May 8, 2016, San Diego, California.