Knowledge about cancer biology is extending and has meaningful repercussions on patients' care. Therefore, there is a growing need to assess tumor biology not only at diagnosis, but also throughout the course of management. Tumor tissue biopsies are particularly useful, but are not convenient for repetitive analyses because of the need for invasive procedures. Advances in biotechnology allow currently getting more and more information from liquid biopsies, based on small amounts of tumor material released for instance into the peripheral blood. Already used in the treatment of non-small cell lung cancers, these new techniques represent more generally an important step forward for personalized oncology.