Blood-based biomarkers such as Circulating Tumor Cells (CTCs), circulating free tumor DNA (cfDNA) and microRNAs (miRNAs) have the potential to improve the development of personalized medicines for cancer patients. This is of particular importance when biopsies of the primary tumor or metastases are not accessible (e.g. at early disease stages or in minimal residual disease) or possible and the associated risk of adverse events when taking a biopsy is high. Furthermore, a longitudinal follow-up of disease markers is desirable to improve prognosis or to monitor treatment efficacy. CANCER-ID aims to validate technologies for CTCs, cfDNA and miRNAs to determine the absence/presence of drug targets and assess the response to treatment. Important challenges for all circulating biomarker development are assay sensitivity, specificity and assay standardization and validation. In three project phases (pre-evaluation, technical assay validation and clinical validation) the CANCER-ID consortium aims at the development and validation of Standard Operating Procedures (SOPs) for technologies assessing blood-based biomarkers. In the pre-evaluation phase, four working groups will be established that will evaluate biomarker technologies and set the criteria to be met for any technology before moving to the next phase. In the Technical Evaluation Phase, the technologies identified as promising in the pre-evaluation phase will be implemented and tested at the sites of the consortium members using blood samples taken from patients with metastatic carcinomas and healthy controls. In order to prove broader applicability and clinical utility of the consortium’s technologies and protocols, the validated assays will be deployed in controlled clinical studies (TRACERx, NVALT-17, SPECTAlung; patients under SoC treatment) in 1) Non-Small Cell Lung Cancer (NSCLC) and 2) anti-Her2-resistant metastatic breast cancer (Her2RMBC). The two indications were chosen based on medical need and economic impact, technical considerations and access to clinical samples.The combination of 17 academic groups (ten large clinical trialsites), 6 EFPIA companies with extensive experience in the use of blood-based biomarkers in clinical trials, 5 SMEs with unique technologies for CTC isolation (Vycap, Leukocare, Gilupi) or for creation of databases, analysis of complex molecular information and data management (Alacris, TATAA) and two non-profit organizations (IBBL, a Biobank with extensive experience in the validation and execution of plasma assays; EORTC, the European organization that aims to develop, conduct, coordinate, and stimulate translational and clinical research) comprises a unique network of experts in the fields of tumour biology, biomarker development, clinical sciences and bioinformatics. In addition, regulatory agencies and patient advocacy groups are involved from the beginning of the project. The academic leaders of this consortium, Klaus Pantel, who published more than 300 reports and high impact review articles on disseminating tumor cells, and Leon Terstappen, leader of the FDA-approved benchmark CellSearch CTC detection system, are the pioneers of this field. In addition, both have extensive experience with coordination of EU projects in the field (Pantel: DISMAL, CTC-SCAN; Terstappen: CTCTrap). This is complemented by the IMI and FP7 project management experience of the EFPIA project coordinator, Thomas Schlange (Bayer Pharma AG). He will be supported by Barbara Baggiani from Menarini/Silicon Biosystems (developer and vendor of the DEPArray).