Cancer for many patients is still a lethal disease, and we are at the edge of the time that it will be the leading cause of death in the western world. One of the hallmarks of cancer is its ability to spread to other organs, turning cancer in essence to a systemic disease. For this reason, systemic therapy plays an important role in our efforts to either obtain cure or to prolong life and palliate symptoms. The ultimate goal in the development of such new treatments is cure or prolongation of life, but the process to ascertain this may be lengthy. This presents a limitation to the rapid assessment of the potential benefit of new cancer treatments, which is why investigators and regulators have been interested in clinical trial measures that could provide early readouts of drug activity or efficacy, in other words for surrogate indicators for the ultimately desired outcome.