Abstract
165 Background: In order to optimize molecular screening in advanced prostate cancer patients, we implemented a prospective molecular triage trial PETRUS (NCT01786031), based on molecular characterization of fresh tumor biopsies and circulating tumor cells (CTCs) in patients with mCRPC. The primary objective was to investigate the feasibility of prospectively performing molecular profiling of CRPC patients. Methods: A tumor biopsy from a metastatic and tumor primary site, along with blood samples specimen were collected from patients, and both frozen and FFPE samples were obtained. CTCs were detected using two methods, CellSearch and filtration (ISET, isolation by Size of Epithelial Tumor cells) combined to four-color immunofluorescent staining. Results: From December 2012 and March 2014, 51 CRPC patients with metastases accessible for biospy were included in 5 centres in France. Tumor biospy were successful (≥ 50% tumor cells) in 36/51 pts (72%). CTCs with different phenotypes were detected by CellSearch and ISET combined to four-color immunofluorescent staining in 28 (51%) pts. FISH AR and ERG was successful in only 54% and 32% of metastasis biopsies and primitive tumors respectively, most likely due to the absence of tumor cells or overfixation. The ISET platform was able to detect CTCs clusters, CTCs expressing epithelial and vimentin markers. AR amplification and ERG rearrangement analyses showed high level of heterogeneity with evidence of multiple CRPC iCTC subpopulation. A high level of heterogeneity between CTCs, metastasis biopsies and primitive tumors was observed for ERG rearrangement and AR amplification status. Conclusions: Our results demonstrate that CTCs could be an alternative source for surrogate molecular marker assessment in mCRPC, but neither approach could truly reflect the extreme heterogeneity observed in CTCs from mCRPC. Our preliminary results suggest also the operational feasibility of metastatic tumor biopsy: high interest for patients, significant yield of tumor biopsies and ad hoc molecular analysis. Clinical trial information: NCT01786031.
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