Molecular characterization of circulating tumor cells (CTC) and CTC subpopulations in baseline and progressive metastatic castration resistant prostate cancer (mCRPC).

132 Background: Numerous resistance mechanisms have been postulated in progressive mCRPC. Determining the presence of putative predictive biomarkers in patients requires a real-time tumor assessment because the biology changes under the influence of the specific therapy(ies) that a patient (Pt) has received. We examined CTC and CTC subpopulation incidence and molecular characterization of tumors from Pts with progressive mCRPC to assess if determinants of resistance can be assessed through a CTC test. Methods: 48 samples from 21 unique progressive mCRPC pts treated with androgen receptor targeted (AR tx) therapies, 9 (43%) on Abiraterone plus Prednisone (AA+P) and 12 (57%) on Enzalutamide (E). Samples were collected and shipped to Epic Sciences, where cells were stained and CTC identified by fluorescent scanners and algorithmic analysis. CTCs, defined as classic (CK+ CD45- w/intact DAPI nuclei and distinct), apopotic (CK+, CD45-, non-intact nuclei) and CK- (CK-, CD45-, intact and distinct) were identified...