Detection and Characterization of Circulating Tumour Cells from Frozen Peripheral Blood Mononuclear Cells

David Lu1, Ryon P. Graf1, Melissa Harvey1, Ravi A. Madan2, Christopher Heery2, Jennifer Marte2, Sharon Beasley1, Kwong Y. Tsang2, Rachel Krupa2, Jessica Louw1, Justin Wahl1, Natalee Bales1, Mark Landers1, Dena Marrinucci1, Jeffrey Schlom2, James L. Gulley2 and Ryan Dittamore1
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Retrospective analysis of patient tumour samples is a cornerstone of clinical research. CTC biomarker characterization offers a non-invasive method to analyse patient samples. However, current CTC technologies require prospective blood collection, thereby reducing the ability to utilize archived clinical cohorts with long-term outcome data. We sought to investigate CTC recovery from frozen, archived patient PBMC pellets. Matched samples from both mCRPC patients and mock samples, which were prepared by spiking healthy donor blood with cultured prostate cancer cell line cells, were processed “fresh” via Epic CTC Platform or from “frozen” PBMC pellets. Samples were analysed for CTC enumeration and biomarker characterization via immunofluorescent (IF) biomarkers, fluorescence in-situ hybridization (FISH) and CTC morphology. In the frozen patient PMBC samples, the median CTC recovery was 18%, compared to the freshly processed blood. However, abundance and localization of cytokeratin (CK) and androgen receptor (AR) protein, as measured by IF, were largely concordant between the fresh and frozen CTCs. Furthermore, a FISH analysis of PTEN loss showed high concordance in fresh vs. frozen. The observed data indicate that CTC biomarker characterization from frozen archival samples is feasible and representative of prospectively collected samples.