"Chemotherapy is slowly being supplemented by a new generation of drugs that recognize specific targets in or on cancer cells and has proven to be more effective with markedly fewer side effects. During the course of the disease alternative oncogenic signaling pathways take over inevitably leading to drug resistance. As a consequence renewed tumor analysis is required to redefine the optimal treatment regiment. However a biopsy can frequently not be obtained without risk and or discomfort to the patient. Circulating tumor cells (CTC) may circumvent this problem.CTC refer to cells that detach from a primary tumor or metastatic site, circulate in the peripheral blood and may form metastasis. CTC represent a ""liquid biopsy"" that can be used to tailor treatment for individual patients. CTC are however rare and can only be obtained for further characterization in a small fraction of patients.In the CTCtrap consortium universities, research institutions and SMEs are linked in a common effort, starting from the simple, but innovative view of using Therapeutic Apheresis (TA), as a way to collect CTC from peripheral blood in cancer patients.A new TA column will be developed to capture CTC and then reintroduce the blood devoid of tumor cells back into the body with the promise to obtain CTC in all patients at risk for recurrence or diagnosed with metastatic disease. The molecular characterization of these CTC is expected to gather new knowledge on metastasis' mechanism, provide a risk assessment and the optimal therapy choice during the course of the disease of cancer patients. The new knowledge on CTC heterogeneity within cancer type and within individuals will allow for the tuning of CTCapheresis to specific cancer types. Prospective pilot studies will be setup to investigate the feasibility of the CTCapheresis in the clinic and their potential therapeutic benefit.Success of CTCapheresis will lead to a radical change in the diagnosis and treatment of solid tumors."