Evaluation Of Pten Status In Circulating Tumor Cells (Ctcs) And Matched Tumor Tissue From Patients With Castrate-Resistant Prostate Cancer (Crpc)

62 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. We evaluated PTEN status in archived tissue, metastatic bone biopsies, and CTCs from CRPC patients. Here we report the results of PTEN evaluation in CTCs from 42 CRPC patients and matched tissue from 6 patients with more underway.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 ≥5 CTCs per 2 slides (74%) were then tested for PTEN by FISH. Partial loss was defined as a decrease in PTEN copies (PTEN < CEP10) and total loss as zero PTEN copies. PTEN IHC in tissue was stained using CST clone 138G6 and H-scores ≤ 200 counted as loss.Partial or total loss of PTEN by FISH was observed in 15 of 31 patients (48%) by CTC analysis. Changes in ploidy were frequently observed and broad heterogeneity seen both within and between patients. Weighted across patients, the most frequently observed abnormal genotypes in CTCs were 2 CEP10/0 PTEN (total loss, diploid, 5.8%), 3 CEP10/0 PTEN (total loss, triploid, 4.5%), and 3 CEP10/3 PTEN (PTEN-normal, triploid, 4.2%). These genotypes were not observed in over 1,000 white blood cells evaluated evenly across 31 patients, demonstrating that cells identified as CTCs on the Epic platform show malignant features not observed in normal cells. PTEN loss was detected by IHC in 6 of 8 (75%) archived patient samples and 7 of 8 (87%) of matched bone biopsies. Where CTCs were available (6 cases), PTEN status was correctly determined as lost in 4 cases, normal in 1 case and borderline in one case.Our results illustrate the high percentage of PTEN loss in CRPC patients and the potential for using CTCs as a non-invasive, real-time biopsy to determine a patient's PTEN status. PTEN status will be determined using these assays in an upcoming AKT inhibitor Phase II trial.