Opportunities and pitfalls of cancer imaging in clinical trials.

Cancer treatment strategies have changed considerably over the past two decades, with increasing emphasis on cancer-specific biological therapies. This situation has led to the incorporation of biomarkers, including those obtained by medical imaging, into trial designs to better understand mechanisms of action and, hopefully, to provide early evidence of treatment efficacy at a molecular or physiological level. Unlike blood tests and tissue samples, an imaging biomarker allows assessment of treatment in the whole tumor, in all tumors in the body, and at multiple time points. This situation has increased the complexity of clinical trials, as each imaging modality has issues related to cost, ease of use, patient compatibility, data analysis, and interpretation. This article reviews strengths and limitations of the current imaging methods available in clinical cancer trials, including MRI, CT, PET, and ultrasonography. The information gained by each test, and the difficulties in acquiring the data and interpreting it are also discussed in order to help researchers plan imaging in clinical trials and interpret data from such studies.