Circulating tumour cells (CTCs) are becoming very welcome in the field of oncology, and they are also promising in the clinical field, in the area of drug development. Proof of concept that CTCs may correlate with the prognosis of cancer has been completed for many types already. Also, the CTCs may carry information that is relevant to the disease progression and behaviour and this data cannot be obtained from the primary tumour. Hence they are becoming extremely valuable in the field of drug development and evaluation of candidate medications in pharmaceutical research and industry. Dr Ioannis Papasotiriou, MD at RGCC, discovers the contribution of circulating tumour cells in drug development.