Efficacy of Cabazitaxel in Castration-resistant Prostate Cancer Is Independent of the Presence of AR-V7 in Circulating Tumor Cells

Androgen receptor splice variant 7 (AR-V7) in circulating tumor cells (CTCs) from patients with metastatic castration-resistant prostate cancer (mCRPC) was recently demonstrated to be associated with resistance to abiraterone and enzalutamide.

Cabazitaxel might, however, remain effective in AR-V7-positive patients.

To investigate the association between AR-V7 expression in CTCs and resistance to cabazitaxel.

We selected patients with mCRPC from the multicenter, randomized, phase 2, randomized, open-label, multicenter study in mCRPC on the pharmacodynamic effects of budesonide on cabazitaxel (Jevtana) (CABARESC). Before the start of the first and third cabazitaxel cycle, CTCs were enumerated using the CellSearch System. In patients with ≥10 CTCs in 7. 5ml blood at baseline, the expression of AR-V7 was assessed by quantitative polymerase chain reaction.

The primary end point was the association between the AR-V7 status and the CTC response rate (decrease to fewer than five CTCs in 7. 5ml blood during treatment). Secondary end points were the prostate-specific antigen (PSA) response rate (RR) and overall survival (OS). Analyses were performed using chi-square and log-rank tests.

AR-V7 was detected in 16 of 29 patients (55%) with ≥10 CTCs and was more frequently found in abiraterone pretreated patients (5 of 5 [100%] treated vs 7 of 20 [35%] untreated; p=0. 009). We found no differences in CTC and PSA RRs. The presence of AR-V7 in CTCs was not associated with progression-free survival (hazard ratio [HR]: 0. 8; 95% confidence interval [CI], 0. 4-1. 8) or overall survival (HR 1. 6; 95% CI, 0. 6-4. 4).

The response to cabazitaxel seems to be independent of the AR-V7 status of CTCs from mCRPC patients. Consequently, cabazitaxel might be a valid treatment option for patients with AR-V7-positive CTCs.

Tools are needed to select specific treatments for specific patients at specific times. The presence of the gene AR-V7 in CTCs has been associated with resistance to anti-androgen receptor treatments. We investigated whether this holds true for cabazitaxel, but we found cabazitaxel to be effective independent of the presence of AR-V7.

European urology. 2015 Jul 15 [Epub ahead of print]

Wendy Onstenk, Anieta M Sieuwerts, Jaco Kraan, Mai Van, Annemieke J M Nieuweboer, Ron H J Mathijssen, Paul Hamberg, Hielke J Meulenbeld, Bram De Laere, Luc Y Dirix, Robert J van Soest, Martijn P Lolkema, John W M Martens, Wytske M van Weerden, Guido W Jenster, John A Foekens, Ronald de Wit, Stefan Sleijfer

Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. Electronic address: w. onstenk@erasmusmc. nl. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Sint Franciscus Gasthuis, Department of Internal Medicine, Rotterdam, The Netherlands. , Gelre Ziekenhuizen, Department of Internal Medicine, Zutphen, The Netherlands. , GZA Hospitals Saint Augustinus, Wilrijk, Belgium; Center for Oncological Research, University of Antwerp, Antwerp, Belgium. , GZA Hospitals Saint Augustinus, Wilrijk, Belgium; Center for Oncological Research, University of Antwerp, Antwerp, Belgium. , Erasmus MC, Department of Urology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus MC, Department of Urology, Rotterdam, The Netherlands. , Erasmus MC, Department of Urology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands. , Erasmus Medical Center Cancer Institute and Cancer Genomics Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands.

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