209 Background: Circulating tumor cell (CTCs) are traditionally defined as EpCAM/CK+ cells, CD45-, and morphologically distinct. However, recent evidence suggests that other populations of CTC candidates exist including cells that are EpCAM/CK- or smaller in size than traditional CTCs. CTC positive selection techniques that isolate CTCs based on size, density, or EpCam positivity may miss subpopulations. We aimed to molecularly characterize novel CTC candidates utilizing the Epic Sciences platform, which performs no physical selection. Methods: Blood from 10 healthy volunteers (HV) and 39 patients (pts) with metastatic castration-resistant prostate cancer (mCRPC) were collected and shipped to Epic Sciences, where all nucleated cells were plated onto glass slides and subjected to immunofluorescence (IF) staining and CTC identification by fluorescent scanners and algorithms. Traditional CTCs were identified as CK+CD45- cells with intact DAPI nuclei and after pathologist review of their morphology. Candidate CK- CTC populations were identified as CK-CD45- that were morphologically malignant. Small nuclear size candidate CTCs were identified as CK+CD45- cells with diameters similar to or smaller than that of a typical white blood cells (WBCs). All candidate CTC were evaluated with prostate cancer relevant biomarkers, including androgen receptor (AR) by IF and PTEN loss and ERG rearrangements by FISH. Results: Thrity eight out of 39 pts had one or more traditional CTCs/mL and 36 out of 39 pts had one or more CK- CTCs/mL of blood. Eight out of 39 samples had more than 10 CK- CTCs/mL. Fifteen out of 39 samples had evidence of small nuclear size CTCs at varying incidences and sizes of cells. We observed PCa biomarkers including high AR expression, PTEN deletion, and ERG rearrangements in both CK- and small nuclear size CTCs. These features were not observed in over 1,000 WBCs evaluated and HV. Conclusions: Candidate CTC that are CK-CD45- and/or with a small nucleus are identified on the Epic Sciences platform in blood from mCRPC pts. Studies are ongoing to determine their clinical relevance.
Circulating Tumor Cell Analysis in Patients with Progressive Castration-Resistant Prostate Cancer