Purpose: The use of circulating tumor cells (CTC) as "liquid biopsy" is limited by the very low yield of CTCs available for subsequent analyses. Most in vitro approaches rely on small sample volumes (5-10 mL).Experimental Design: Here, we used a novel approach, the GILUPI CellCollector, which enables an in vivo isolation of CTCs from peripheral blood. In total, 50 lung cancer patients were screened in two subsequent device applications before and after therapy (n ¼ 185 applications).Results: By in vivo isolation, 58% (108/185) of the patients were positive for !1 CTC (median, 5 CTCs; range, 1-56 cells) as compared with 27% (23/84; range, 1-300 cells) using the FDAcleared CellSearch system. Furthermore, we could show that treatment response during therapy was associated with significant decreases in CTC counts (P ¼ 0.001). By dPCR, mutations in the KRAS and EGFR genes relevant for treatment decisions could be detected in CTCs captured by in vivo isolation and confirmed in the primary tumors of the same patients.Conclusions: In vivo isolation of CTCs overcomes blood volume limitations of other approaches, which might help to implement CTC-based "liquid biopsies" into clinical decision making.

Aim: Liquid biopsy -isolating and analysing circulating tumour cells (CTCs) from the blood of lung cancer patients -can provide additional information on prognosis, treatment efficacy and molecular tumour evolution. Currently, CTCs are isolated in vitro from limited volumes of patient blood samples. To overcome this limitation, an innovative device, the GILUPI CellCollector TM , was used to isolate CTCs in vivo. Here, we conducted a comprehensive study deploying this effective device, to monitor CTC counts before initiation of chemotherapy and 12 weeks after in 50 lung patients. Further, we investigated the reproducibility of results, the correlation of the clinical response to CTC number changes, and mutations in CTCs of patients with known mutations in the primary tumour. Patients and methods: 50 lung cancer patients (48 NSCLC and two SCLC) were screened for CTCs by two subsequent device applications before therapy initiation and 12 weeks after (n = 185 applications in total). Additionally, blood samples were analysed with the CellSearch® system. The CTC count change before and after therapy was correlated with clinical response. To analyse cancer specific mutations in CTCs captured with the GILUPI CellCollector TM , digital PCR (dPCR) was performed.Results: Applying the GILUPI CellCollector TM , CTCs were isolated from 78% of the patients during the pre-therapy visit. Overall, successful isolation of CTCs was significantly more frequent with the GILUPI CellCollector TM (58%) compared to CellSearch® (28%). Furthermore, by using the GILUPI CellCollector TM for CTC quantification before and after therapy initiation, an indication for responsive and non-responsive treatment outcomes was seen. Further, we were able to detect KRAS and EGFR mutations in CTCs known to be present in the primary tumour biopsy material. Conclusions: The GILUPI CellCollector TM overcomes blood volume limitations of other diagnostic approaches and thereby increases the diagnostic sensitivity of CTC isolation. It allows enumeration and molecular analysis of CTCs which might help to monitor therapy efficacy and improve treatment strategies. Disclosure: K. Lücke: Is founder, shareholder and CEO of GILUPI GmbH and also patentee of the GILUPI CellCollectorTM. All other authors have declared no conflicts of interest.

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