Abstract A60: Evaluation of preanalytic variables in liquid biopsy tests for prostate cancer: Specimen acquisition and patient context factors that impact results
Authors: Tsui Dana , Barnett Ethan S. , Bramlet Kelli , Schonhoft Joseph , Rizzi Ruben , Scher Howard I. 
Published: June 2020

Abstract
Cell-free DNA (cfDNA) and circulating tumor cell (CTC) enumeration and profiling serve as sources of tumor material to guide treatment decisions. Use of blood-based biomarker assays requires an understanding of factors outside the laboratory where the assay is performed that can influence the final reported result. The factors include preanalytical variables related to specimen acquisition, delivery and storage, and patient context variables. To address this question, our group activated an IRB-approved protocol to study the effect of variables associated with the factors mentioned above, including: (i) the order of blood being drawn in a single collection, (ii) collections done at different times of the day, (iii) collections repeated 1-14 days apart, (iv) patient fasting status, and (v) glucocorticoid use as an antiemetic. Our focus is on validated assays spanning different contexts of use in metastatic prostate cancer management, including: 1) a nuclear localized AR-V7 assay in circulating tumor cells (CTCs) as response indicator to androgen receptor (AR) signaling inhibitor vs. taxane based chemotherapy in the second line of therapy (Epic Sciences®, San Diego, CA); 2) a change in CTC number from any pretherapy value to zero post-therapy as a response indicator (CellSearch®, Menarini Silicon Biosystems); and 3) the detection of somatic mutations and copy number alterations in the AR pathway as resistance mechanism to abiraterone acetate in castration-resistant prostate cancer patients. Our pilot data currently include a cohort of 12 patients on which we aimed to study the effect of draw order on (i) the counts of CTC and ARV7 expression assessed by EpicScience® and (ii) the quality and quantity of cfDNA and mutation detected assessed by the analytically validated ThermFisher Oncomine® Pan-cancer cfDNA assay (Waltham, MA). Our initial analysis showed that the CTC and cfDNA results are mostly consistent across different draw orders, with slight variation at levels close to or below the limit of detection of the assay involved (such as 0.1% variant allele frequency of the ThermoFisher Oncomine® assay). We are expanding the sample size to further validate these results, perform additional statistical analysis, and include data from the Food and Drug Administration (FDA) cleared, CellSearch® CTC enumeration assay and MSK-ACCESS (Analysis of Circulating cfDNA to Examine Somatic Status), an ultrasensitive 129-gene cfDNA profiling assay that was developed internally at Memorial Sloan Kettering Cancer Center, recently approved by the New York State Department of Health, and launched in our Clinical Laboratory Improvement Amendment (CLIA)-certified molecular diagnostic laboratory. The results of this study will provide evidence to inform the design of preanalytical sample collection and inform how to use these tests in clinical practice.
Citation Format: Dana Tsui, Ethan S. Barnett, Kelli Bramlet, Joseph Schonhoft, Ruben Rizzi, Howard I. Scher. Evaluation of preanalytic variables in liquid biopsy tests for prostate cancer: Specimen acquisition and patient context factors that impact results [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr A60.