The RECIST (Response Evaluation Criteria in Solid Tumors) criteria: implications for diagnostic radiologists.

Abstract

Monitoring response of tumours to treatment is an integral and increasingly important function of radiologists working in oncological imaging. Imaging studies play a pivotal, objective role in quantifying tumour response to a variety of physical and pharmaceutical treatments. Objective tumour shrinkage has been widely adopted as a standard end-point to select new anti-cancer drugs for future study, as a prospective end-point for definitive clinical trials designed to estimate the benefit of treatment in a specific group of patients, and is widely used in everyday clinical practice to guide clinical decision-making. In the late 1970s it became apparent that a common language was necessary to report the results of cancer treatments in a consistent manner. Standardized criteria for measuring therapeutic response were adopted in 1981 but have been modified by various cancer organizations [1–3]. The World Health Organisation (WHO), the National Cancer Institute and the European Organisation for Research and Treatment of Cancer have recently adopted a new set of tumour response criteria (Response Evaluation Criteria in Solid Tumours (RECIST)) [4]. The RECIST criteria have been introduced to unify response assessment criteria, to define how to choose evaluable lesions and to enable the use of new imaging technologies (spiral CT and MRI). The RECIST documentation goes beyond lesion selection, measurement and assessment of response. It also makes specific recommendations on the usage of imaging techniques. The CT protocols are particularly detailed (imaging parameters for incremental and spiral machines, use of contrast enhancement and the presentation of images). The implications of this document are wide ranging and are likely to have cost and manpower implications for radiology departments in cancer treatment centres. This Commentary highlights these issues. The RECIST response criteria are largely based on a retrospective statistical evaluation of measurements (not original imaging data) obtained in eight pharmaceutical-sponsored clinical trials where 569 patients were assessed for tumour response [5]. The data analysed were selected by their ‘‘availability’’ but did have a broad range of tumours and serial measurements, with outcomes recorded. The quality control of the measurements themselves is unknown. In an attempt to simplify tumour measurements, unidimensional and bidimensional evaluations were compared and the new criteria selected are chosen because of the link between change in diameter, product and volume of spherical lesions (Table 1). It has recently been noted that the two measurement methods continue to show good concordance for 4613 patients [6]. The new RECIST response criteria are designed to replace existing WHO criteria; the two sets of criteria are compared in Table 2. It is important to note that the RECIST criteria still rely on size change of lesions to make response assessments. RECIST acknowledges that tumour shrinkage may not be an appropriate end-point in the investigation of new cytostatic agents currently in phase 1 and 2 clinical trials [7]. RECIST guidance defers the issues relating to functional tumour response and unique complexities of specific tumours or anatomical sites. There