Introduction/ObjectivesMetastatic castration-resistant prostate cancer (mCRPC) is a heterogen disease. Since most prostate cancer patients have a biopsy performed only at the time of diagnosis, representative tumor tissue sample giving real time information about the disease status is generally missing. CTC enumeration is a biomarker associated with clinical outcomes in patients with mCRPC. However, capturing these rare cells from whole blood is still a major challenge because they are extreme rare. Futhermore CTCs may exhibit a feature of epithelial-mesenchymal transition. First we assessed the method is best suited for the isolation of CTCs in mCRPC patients. Additionally was to evaluate the association between CTCs counts and ERG rearrangement in tumor samples.

Materials & Methods

A tumor sample from metastatic site, along with blood samples were collected from mCRPC patients. Tumor samples were characterized of ERG rearrangement by fluorescence in situ hybridization. CTCs were detected using two methods. One was SreenCells system, CTC isolation based on size exclusion. The second method was the CellCollector which CTC captured using monoclonal specific antibody to EpCAM. This system can be used for CTC isolation ex vivo and in vivo. We used it here ex vivo. Captured CTCs were identified based on histological cell architecture by immunofluorescence staining using cytokeratin (8, 18, 19) and nuclear Hoechst staining positive as well as CD45 negative as criteria to exclude EpCam positive leucocytes

Results

We obtained duplicate blood samples from 10 mCRPC patient using SreenCells system and CellCollector isolation methods. Bothe methods detected CTCs in 8 of 10 blood samples, detection rate is 80 %. ScreenCells isolated in average of 22.6 CTCs (range of 0-80 CTCs). The CellCollector captured CTCs ex vivo in average of 3 CTCs (range of 0-6 CTCs). In a direct comparison of the ScreenCell system and the Cellcollector is significant different (p 0.0156) in the CTC counts. The CTC number of both systems is moderate correlated (r 0.5). All mCRPC tissue samples harbored an ERG rearrangement in range of 89 until 98 %. The CTC number of the ScreenCell system is good correlate with PSA level (r 0.776) and also with the ERG- rearrangement (r 0.5) of tissue samples.

Conclusion

Our results demonstrate that CTC isolation based on the physical properties has a higher sensitivity as the CTC isolation technique based on the biological cell properties in mCRPC patients. The size exclusion technique coupled with characterization of specific staining morphologies might be used to identify a heterogeneous CTC population which is always present in advanced cancer. It should be decided in dependence of the advanced cancer stage which CTC isolation technique can be used. The cost of the material and the hours of work are equal in both systems.

Citation Format: Gerit Theil, Christine Weiss, Kersten Fischer, Andre Schumann, Paoloa Fornara. Heterogeneity in circulating tumor cells in blood samples of metastatic castration-resistant prostate cancer patient: comparison of isolation technique [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3929. doi:10.1158/1538-7445.AM2017-3929