Comparison of circulating tumor cell (CTC) capture/identification methods and NanoString evaluation of gene expression in CTCs and cell-free circulating tumor mRNA (cctmRNA) in patients with metastatic lung cancer

Circulating tumor cells (CTC) and cell free circulating tumor mRNA (cctmRNA) can serve as biomarkers for prognosis and treatment response in lung and other cancers. A barrier to CTC use in some cancers is the low numbers of CTC captured, and the low percent of patients with detectable CTCs. Past comparisons of non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) patients have shown larger cohorts of patients with detectable CTCs, and higher CTC numbers, for SCLCs. We compared methods for CTC capture/identification, and profiled mRNA from both the CTCs and cell free plasma RNA (cctmRNA) for to identify tumor-associated biomarkers. Peripheral blood was collected from 10 SCLC and 10 NSCLC patients prior to therapy, and from 4 normal controls. Capture using the standard EpCAM CellSearch reagent (unicapture) was run in parallel with EpCAM plus Her2, EGFR and MUC-1 combined ferrofluid (quadcapture) plus the use of anti-cytokeratin 7 (CK7) to assist in CTC identification. Unicapture detected CTCs in 40% of NSCLC and 60% of SCLC; whereas, quadcapture/CK7 identified 20% CTCs in NSCLC and 80% in SCLC. Overall, the quadcapture did not improve CTC capture efficiency. Exploratory NanoString analysis was performed on cell-free plasma from these patients and the ferrofluid isolated CTCs. Cancer-specific biomarkers were detected in mRNA from plasma and CTCs by NanoString included CCL5, CLU and SRGN. In summary, quadcapture ferrofluid reagent did not improve the capture efficiency, although the addition of CK7 may have the potential to identify additional CTCs. Nanostring analysis of cctmRNA and CTCs mRNA suggested potential new lung cancer biomarkers that require validation in larger studies. Citation Format: Yanis Boumber, Charu Aggarwal, Catherine Thrash-Bingham, Patricia Fittipaldi, Polina Guseva, Ramillya Vlasenkova, Chandra Rao, Jianming Pei, Brian L. Egleston, Hossein Borghaei, Massimo Cristofanilli, Ranee Mehra, Ilya Serebriiskii, R. Katherine Alpaugh. Comparison of circulating tumor cell (CTC) capture/identification methods and NanoString evaluation of gene expression in CTCs and cell-free circulating tumor mRNA (cctmRNA) in patients with metastatic lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1584.