Association of AR-V7 on Circulating Tumor Cells as a Treatment-Specific Biomarker With Outcomes and Survival in Castration-Resistant Prostate Cancer.
OBJECTIVE
A critical decision in the management of metastatic castration-resistant prostate cancer (mCRPC) is when to administer an androgen receptor signaling (ARS) inhibitor or a taxane.


OBJECTIVE
To determine if pretherapy nuclear androgen-receptor splice variant 7 (AR-V7) protein expression and localization on circulating tumor cells (CTCs) is a treatment-specific marker for response and outcomes between ARS inhibitors and taxanes.


METHODS
For this cross-sectional cohort study at Memorial Sloan Kettering Cancer Center, 265 men with progressive mCRPC undergoing a change in treatment were considered; 86 were excluded because they were not initiating ARS or taxane therapy; and 18 were excluded for processing time constraints, leaving 161 patients for analysis. Between December 2012 and March 2015, blood was collected and processed from patients with progressive mCRPC immediately prior to new line of systemic therapy. Patients were followed up to 3 years.


METHODS
Prostate-specific antigen (PSA) response, time receiving therapy, radiographic progression-free survival (rPFS), and overall survival (OS).


RESULTS
Overall, of 193 prospectively collected blood samples from 161 men with mCRPC, 191 were evaluable (128 pre-ARS inhibitor and 63 pretaxane). AR-V7-positive CTCs were found in 34 samples (18%), including 3% of first-line, 18% of second-line, and 31% of third- or greater line samples. Patients whose samples had AR-V7-positive CTCs before ARS inhibition had resistant posttherapy PSA changes (PTPC), shorter rPFS, shorter time on therapy, and shorter OS than those without AR-V7-positive CTCs. Overall, resistant PTPC were seen in 65 of 112 samples (58%) without detectable AR-V7-positive CTCs prior to ARS inhibition. There were statistically significant differences in OS but not in PTPC, time on therapy, or rPFS for patients with or without pretherapy AR-V7-positive CTCs treated with a taxane. A multivariable model adjusting for baseline factors associated with survival showed superior OS with taxanes relative to ARS inhibitors when AR-V7-positive CTCs were detected pretherapy (hazard ratio, 0.24; 95% CI, 0.10-0.57; P = .035).


CONCLUSIONS
The results validate CTC nuclear expression of AR-V7 protein in men with mCRPC as a treatment-specific biomarker that is associated with superior survival on taxane therapy over ARS-directed therapy in a clinical practice setting. Continued examination of this biomarker in prospective studies will further aid clinical utility.
Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York2Department of Medicine, Weill Cornell Medical College, New York, New York.
Howard I
HI
Scher
Epic Sciences, La Jolla, California.
David
D
Lu
Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York.
Nicole A
NA
Schreiber
Epic Sciences, La Jolla, California.
Jessica
J
Louw
Epic Sciences, La Jolla, California.
Ryon P
RP
Graf
Body Imaging Service, Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, New York5Department of Radiology, Weill Cornell Medical College, New York, New York.
Hebert A
HA
Vargas
Epic Sciences, La Jolla, California.
Ann
A
Johnson
Epic Sciences, La Jolla, California.
Adam
A
Jendrisak
Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York6Cancer Services, Department of Medical Oncology, Cork University Hospital, Wilton, Cork, Ireland.
Richard
R
Bambury
Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York2Department of Medicine, Weill Cornell Medical College, New York, New York.
Daniel
D
Danila
Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York.
Brigit
B
McLaughlin
Epic Sciences, La Jolla, California.
Justin
J
Wahl
Epic Sciences, La Jolla, California.
Stephanie B
SB
Greene
Biostatistics Service, Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, New York.
Glenn
G
Heller
Epic Sciences, La Jolla, California.
Dena
D
Marrinucci
Clinical Chemistry Service, Department of Laboratory Medicine, Memorial Sloan Kettering Cancer Center, New York, New York.
Martin
M
Fleisher
Epic Sciences, La Jolla, California.
Ryan
R
Dittamore
D000368:Aged; D000369:Aged, 80 and over; D059002:Androgen Receptor Antagonists / Q000494:pharmacology / Q000627:therapeutic use; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D014408:Biomarkers, Tumor; D003430:Cross-Sectional Studies; D018450:Disease Progression; D019008:Drug Resistance, Neoplasm; D006801:Humans; D007610:Kallikreins / Q000097:blood; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009360:Neoplastic Cells, Circulating / Q000378:metabolism*; D016016:Proportional Hazards Models; D017430:Prostate-Specific Antigen / Q000097:blood; D064129:Prostatic Neoplasms, Castration-Resistant / Q000097:blood* / Q000175:diagnosis / Q000401:mortality / Q000628:therapy; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D012680:Sensitivity and Specificity; D043823:Taxoids / Q000494:pharmacology / Q000627:therapeutic use; D016896:Treatment Outcome
D059002:Androgen Receptor Antagonists; D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D020033:Protein Isoforms; D011944:Receptors, Androgen; D043823:Taxoids; C549870:KLK3 protein, human; D007610:Kallikreins; D017430:Prostate-Specific Antigen