ABSTRACT
Response assessment in oncology, using conventional morphological imaging, relies on tumor shrinkage. This assessment has been standardized using the Response Evaluation Criteria in Solid Tumors (RECIST), which have recently been updated to reflect more accurately the change in volume of spherical lesions.1 Despite this change, RECIST measurements are prone to errors, are particularly difficult for small lesions, and are laborious. Furthermore malignant lesions may be difficult to distinguish from areas of fibrosis.1 Functional imaging using perfusion computed tomography (CTP), dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), [15O]H2O-positron emission tomography (PET), or ultrasound (US) may provide more specific information about changes in tumor biology. Tumor shrinkage may be a valid endpoint for established cytotoxic drugs, but may not be relevant for biological agents under development, which are often cytostatic. In addition, functional imaging may be more sensitive in detecting an early response to treatment and can potentially identify subpopulations of patients enriched for response.
