Chromosomal instability in circulating tumor cells and cabazitaxel resistance in metastatic castration-resistant prostate cancer.

BACKGROUND: Predictive biomarkers to guide chemotherapy decisions for metastatic castration resistant prostate cancer (mCRPC) are lacking. Preclinical studies indicate that circulating tumor cell (CTC) studies of chromosomal instability (CTC-CIN) can predict taxane resistance.

METHODS: The CARD trial randomized subjects with mCRPC progressing within a year of treatment with an androgen receptor pathway inhibitor (ARPI; enzalutamide or abiraterone acetate plus prednisolone/prednisone) to cabazitaxel or the alternative ARPI. As a pre-planned biomarker analysis, CTCs were isolated from blood samples obtained at baseline; cycle two, and end of treatment. Associations between baseline CTC and CTC-CIN counts with imaging-based progression free survival (ibPFS), overall survival (OS), time to prostate-specific antigen (PSA) progression, RECIST 1.1 objective response rate (ORR), and PSA50 response rate (PRR) were assessed.

RESULTS: High baseline CTC-CIN counts significantly associated with worse OS after adjustment for confounding variables (median OS, 15.3 vs 8.9 months; univariate HR, 2.16; 95% CI, 1.52 - 3.06; p < 0.001; multivariate HR, 1.56; 95% CI, 1.01 - 2.43; p = 0.047). Detectable CTC-CIN counts at baseline may predict a lack of ibPFS and OS benefit when comparing cabazitaxel to ARPI.

CONCLUSION: This preplanned biomarker analysis of CARD confirms that CTC-CIN counts are a clinically useful prognostic and predictive biomarker of taxane resistance in mCRPC. Detectable CTC-CIN at baseline defines a patient subpopulation with unmet clinical needs in which alternative therapeutics should be tested.

TRIAL REGISTRATION: CARD ClinicalTrials.gov number, NCT02485691.

FUNDING: Funded by Sanofi and Epic Sciences.