Abstract 4819: Evaluation of PTEN status in circulating tumor cells (CTCs) and matched tumor tissue from castrate-resistant prostate cancer (CRPC) patients

Abstract

Abstract Background: PTEN loss occurs frequently in prostate cancer and may trigger progression to CRPC through activation of the PI3K/AKT pathway. A blood-based assay that determines PTEN status in CRPC patients could enable informed treatment decisions such as the use of a PI3K-targeted therapy. Here we examined the relationship between PTEN status in CTCs and matched archival and fresh tumor biopsies in 43 CRPC patients. Methods: Nucleated cells from CRPC patient blood were plated onto glass slides and subjected to IF staining and CTC identification by high-speed fluorescent scanners at Epic Sciences. CTCs were identified as CK+/CD45- cells with intact DAPI nuclei, and samples with ≥4 CTCs per 2 slides (74%) were then tested for PTEN by FISH. Heterozygous loss was defined as a decrease in PTEN copies (PTEN < CEP10 and < 2 copies) and homozygous loss as zero PTEN copies. PTEN IHC in tissue was stained using CST clone 138G6 and H-scores ≤ 200 counted as loss. Results: Heterozygous or homozygous loss of PTEN by FISH was observed in 16 of 43 patients (37%) by CTC analysis. In addition to loss of PTEN, changes in ploidy were frequently observed and broad heterogeneity seen both within and between patients. The PTEN status in CTCs correlated strongly with the PTEN status in metastatic tissue: All 10 patients that exhibited homozygous PTEN loss in CTCs showed concordant homozygous PTEN loss in fresh biopsies. This correlation extended to three patients that showed correlated mixed homozygous and hemizygous PTEN loss populations in CTCs and tissue. “Drift or change” in PTEN status from archival to fresh biopsies occurred in 15 patients, In 12 of these patients, PTEN status in CTCs was reflective of the status in fresh tissue. Together with PTEN evaluation, the analysis of androgen receptor expression by immunofluorescence and ERG rearrangements by FISH proved feasibility of multiplex biomarker assessment in CTCs. This analysis demonstrated heterogeneity of AR phenotypes and a positive association of ERG rearrangements and PTEN loss in CTCs, consistent with literature reports. Conclusion: Our results illustrate the potential for using CTCs as a non-invasive, real-time biopsy to determine a patient's current PTEN status. PTEN status will be determined using these assays in an ongoing AKT inhibitor Phase II trial. Citation Format: Elizabeth Punnoose, Eric Tucker, Edith Szafer-Glusman, Jin Zhu, Dena Marrinucci, Jessica Louw, Florence Lee, Mikel Kitchen, Natalee Bales, Lukas Amler, Hartmut Koeppen, Premal Patel, Yibing Yan, Ruth Riisnaes, Gerhardt Attard, Johann de Bono. Evaluation of PTEN status in circulating tumor cells (CTCs) and matched tumor tissue from castrate-resistant prostate cancer (CRPC) patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4819. doi:10.1158/1538-7445.AM2014-4819