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A proof-of-concept study to analyze the clinical utility of a circulating tumor cell-based mutation analysis
Franken A.1, Behrens B.2, Reinhardt F.1, Yang L.1, Rivandi M.1, Cieslik J.-P.1, Dietzel F.3, Stoecklein N.H.2, Niederacher D.1, Fehm T.1, Neubauer H.1
1Department of Obstetrics and Gynecology, University Hospital and Medical Faculty of the Heinrich-Heine University Duesseldorf, Düsseldorf, Deutschland, 2General, Visceral and Pediatric Surgery, University Hospital and Medical Faculty of the Heinrich Heine University Duesseldorf, Düsseldorf, Deutschland, 3Department of Diagnostic and Interventional Radiology, University Hospital and Medical Faculty of the Heinrich-Heine University Duesseldorf, Düsseldorf, Deutschland

Background: In the last decades targeted therapy has become the preferred approach to treat breast cancer. However, the predictive utility of the primary tumor is limited and obtaining serial biopsies of metastatic lesions is challenging. Thus, deriving information about the tumor from liquid biopsies e.g. circulating tumor cells (CTCs) is an appealing idea.
Here, we present a proof-of-concept study on five metastatic breast cancer patients for the clinical utility of whole exome sequencing of CTCs
Methods: CTCs were enriched with the CellSearch system, isolated by micromanipulation, and their DNA was amplified by whole genome amplification. For library preparation the Agilent V6 Kit was used. One index patient was observed by a longitudinal, multiparametric liquid biopsy analysis over more than three years, including whole exome sequencing, RNA profiling and in vitro drug testing of cultured CTCs.
Results: Mutations targetable by FDA approved therapies were detected in the PIK3CA, the ESR1 and the AKT1 genes in four patients. Most of these mutations were either absent in the primary tumor or present in only a minor tumor cell subclone. For the index patient, the evolution of the tumor was retraced, resistance mechanisms were identified, and an AKT1 E17K mutation was hypothesized to be the driver of the metastatic process. During a liquid biopsy-guided treatment with everolimus targeting the Akt1 pathway, CTC counts, detected by CellSearch®, dropped by 97.3% accompanied by a stable disease determined by CT/MRI.
Conclusion: Our results give a glimpse on how a CTC-guided therapy might optimize cancer treatment in future.