Circulating Tumor Cell (Ctc) Detection, N-Terminal Androgen (Ar) Characterization, And Pten Loss In Metastatic Or Advanced Castration Resistant Prostate Cancer (Crpc).

195 Background: Detection and characterization of CTCs offers a minimally invasive mechanism for understanding patient response to therapy and disease evolution. Here we describe a proprietary technology platform to examine CTC incidence, N-terminal AR expression, and PTEN loss in metastatic or advanced CRPC patient samples from a phase II clinical trial (GO27983) testing the combination of the AKT inhibitor ipatasertib and abiraterone. Methods: Blood samples from CRPC patients (n = 283) were collected at screening and shipped to Epic Sciences. Upon receipt, the nucleated cells were plated onto microscope slides and stored at -80C. Two slides were thawed per patient and analyzed with an N-terminal AR CTC assay. CTCs were detected using a combination of CD45 exclusion, CK and N-terminal AR expression, and morphologic criteria. Traditional (CD45-, CK+, DAPI+) and Non-Traditional (CD45-/CK- with distinct morphology or CD45-/CK+ with fragmented nuclei) CTCs were enumerated and N-terminal AR expression was qua...