ABSTRACT

Radiographic changes of tumors treated with newer generations of cytostatic agents do not necessarily occur at the same magnitude or speed as observed in those treated with classic cytotoxic drugs (1-4). As a result, investigators have, to a certain extent, become dissatisfied with the use of traditional imaging response assessment criteria since they do not always adequately capture the effects of novel therapies on primary tumors and metastases (5-8). Furthermore, tumor response to such targeted therapies may not be detected by changes in size but rather by analysis of cystic change, central necrosis, and/or metabolic changes. As greater numbers of anti-cancer therapies are introduced into clinical practice and even greater numbers of experimental anti-cancer drugs enter clinical trials, there is an urgent need for the development and validation of accurate and early imaging surrogate endpoints to assess both the efficacy and safety of these novel target drugs. Improving imaging biomarkers will not only help the individual patient but may also shorten the time for developing a successful anti-cancer therapy by improving statistical power, decreasing the clinical trial duration, and reducing the funding spent in the costly drug development process. Among the promising imaging biomarkers, functional imaging techniques such as 18 F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) and fluoro-L-thymidine positron emission tomography (FLT PET) show tremendous potential. In some instances, FDG PET can help stratify certain types of cancer patients who are most likely respond to a specific treatment and also predict early patient survival.