Development of an immunofluorescent AR-V7 circulating tumor cell assay – A blood-based test for men with metastatic prostate cancer

David Lu; Rachel Krupa; Melissa Harvey; Ryon P. Graf; Nicole Schreiber; Ethan Barnett; Emily Carbone; Adam Jendrisak; Audrey Gill; Sarah Orr; Howard I Scher; Joseph Daniel Schonhoft

doi:10.33393/jcb.2020.2163

Authors

David Lu Epic Sciences, San Diego, California and Exact Sciences, Madison, Wisconsin - USA
Rachel Krupa Epic Sciences, San Diego, California - USA
Melissa Harvey Epic Sciences, San Diego, California - USA
Ryon P. Graf Epic Sciences, San Diego, California - USA
Nicole Schreiber Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York and Prostate Cancer Clinical Trials Consortium, New York, New York - USA
Ethan Barnett Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York - USA
Emily Carbone Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York - USA
Adam Jendrisak Epic Sciences, San Diego, California - USA
Audrey Gill Epic Sciences, San Diego, California - USA
Sarah Orr Epic Sciences, San Diego, California - USA
Howard I Scher Genitourinary Oncology Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, New York and Department of Medicine, Weill Cornell Medical College, New York, New York - USA
Joseph Daniel Schonhoft Epic Sciences, San Diego, California - USA

DOI:

https://doi.org/10.33393/jcb.2020.2163

Keywords:

AR-V7, Castration-resistant prostate cancer, Circulating tumor cells (CTCs), Predictive biomarkers

Abstract

Introduction: Here we describe the development of a protein immunofluorescent assay for the detection of nuclear-localized androgen receptor variant 7 (AR-V7) protein within circulating tumor cells (CTCs) identified in patient blood samples. Used in the clinic, the test result serves as a validated biomarker of futility for patients with progressing metastatic castration-resistant prostate cancer (mCRPC) who are treated with androgen receptor targeted therapies (AATT) in whom nuclear-localized AR-V7 CTCs are identified and have received level 2A evidence in the 2019 National Cancer Center Network (NCCN) guidelines (v1.0).

Methods: Assay development was completed on the Epic Sciences rare cell detection platform using control cell lines of known AR-V7 status and clinical testing of mCRPC patient samples obtained at the decision point in management.

Results and conclusions: Using these samples, all assay parameters, scoring criteria, and clinical cutoffs for positivity were prospectively selected and locked. After assay lock, blinded clinical validation testing was initiated on multiple, independent, clinical cohorts as reported by Scher et al (JAMA Oncol. 2016;2:1441-1449; JAMA Oncol. 2018;4:1179-1186) and Armstrong et al (J Clin Oncol. 2019;37:1120-1129).

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