Sequential monitoring and characterization of circulating tumor cells (CTCs) using the epic sciences platform in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) treated with recently approved therapeutics.

78 Background: The enumeration and molecular characterization of circulating tumor cells (CTCs) may allow sequential evaluation of drug-induced changes and mechanisms of drug resistance that cannot be practically performed by tissue biopsies. Methods: We utilized the Epic Sciences platform to identify and characterize traditional CTCs (CK-CD45+) and other CTC subpopulations (CK-CD45- CTCs and small CTCs) in sequential samples obtained from metastatic castration-resistant prostate cancer (mCRPC) patients (pts) receiving abiraterone acetate (AA), enzalutamide (E), or cabazitaxel (C). Peripheral blood was collected pre-treatment, during treatment (at 1 to 4 weeks, to evaluate pharmacodynamics effects) and at progression. Nucleated cells were plated onto glass slides and subjected to immunofluorescence staining for CK, CD45, and AR, and CTC identification by fluorescent scanners. CTCs from a subset of patients were tested for PTEN loss and ERG rearrangements by FISH. CTCs from a second blood sample collected ...