The early assessment of a solid tumor's response to conventional or new drug therapy to complement or replace current RECIST (or other clinical) criteria remains an elusive goal. The work horse PET tracer (18)F-FDG, may represent the most immediate method to track individual tumor response to therapy for many types of cancer. Newer radiotracers such as radiolabeled annexin V, have also shown the ability to selectively localize to tumor cells undergoing apoptosis (programmed cell death) in response to successful treatment in vivo. In this article we will review therapy reduced tumor apoptosis and the radiotracers used to date to image this process in both animal models and clinical trials.