Expression of AR-V7 and ARv567es in circulating tumor cells correlates with outcomes to taxane therapy in men with metastatic prostate cancer treated in TAXYNERGY

Scott T Tagawa, Emmanuel S Antonarakis, Ada Gjyrezi, Giuseppe Galletti, Seaho Kim, Daniel Worroll, John Stewart, Atef Zaher, Ted P Szatrowski, Karla V Ballman, Katsuhiro Kita, Shinsuke Tasaki, Yang Bai, Luigi Portella, Brian J Kirby, Fred Saad, Mario A Eisenberger, David M Nanus, Paraskevi Giannakakou

Clinical Cancer Research

Biomarkers aiding treatment optimization in metastatic castration-resistant prostate cancer (mCRPC) are scarce. Presence or absence of androgen receptor (AR) splice variants, AR-V7 and ARv567es, in mCRPC patient circulating tumor cells (CTCs) may be associated with taxane treatment outcomes.
Methods:
A novel digital droplet PCR (ddPCR) assay assessed AR splice variant expression in patient CTCs receiving docetaxel or cabazitaxel in TAXYNERGY (NCT01718353). Outcomes were examined according to AR splice variant expression, including prostate-specific antigen (PSA)50 response and progression-free survival (PFS).
Results:
Of 54 evaluable patients, 36 (67%) were AR-V7+, 42 (78%) ARv567es+, 29 (54%) double positive and 5 (9%) double negative. PSA50 response rates at any time were numerically higher for AR-V7- vs AR-V7+ (78% vs 58%; p=0.23) and for ARv567es- vs…