Radiological evaluation of oncologic treatment response: current update

During pharmaceutical trials, clinical, laboratory and imaging methods are frequently used as surrogate endpoints that serve as early indicators of clinical endpoints and to reliably predict clinical outcomes. In cancer patients, objective tumor burden evaluation is commonly accomplished by radiological methods. Radiological monitoring of tumor burden is accurate, easily reproducible and provides an objective evidence of treatment response. During oncology clinical drug trials, change in tumor size has long been considered as a surrogate marker of therapeutic efficacy that provides objective evidence about the drug efficacy and supplements subjective clinical endpoints such as quality of life [1,2]. Drug regulating agencies such as the US Food and Drug Administration (FDA) provide expedited approval of drugs for debilitating and life-threatening illnesses based on radiological evidence of tumor shrinkage [3]. Indeed, the FDA approved capecitabine following a phase-II trial based in part on reduction of tumor burden on CT scans [4]. Since the early 1980s, World Health Organization (WHO) guidelines based on bi-dimensional measurement of tumors have been followed for evaluation of treatment response [5,6]. According to these guidelines, individual tumor size is determined by a ‘cross-product’ obtained by multiplying the longest diameter in the axial plane by its largest perpendicular diameter (Table 1). Baseline and Table 1 Treatment response categories and tumor measurement techniques