Introduction
Overall survival and objective response rates are the usual parameters used to assess response to treatment in cancer patients. Overall survival is the gold standard but the delay necessary to obtain this parameter is too long: physicians need to determine rapidly whether the agent demonstrates encouraging results or not, in order to adjust therapy. In contrast to survival, objective response is more difficult to assess because it is highly dependent on the quality of radiological tumour measurements. Because of the cost and toxicity of treatments, a rigorous evaluation of their efficacy is necessary, as well as evaluation of the toxicity. Many factors interfere with response evaluation, such as the quality and reproducibility of the imaging examinations, the choice of targets and the investigator’s objectivity. International rules for measurement of therapeutic response were progressively established during the 1970s. The WHO (World Health Organization) criteria[1] published by Miller in 1981[2] have been widely adopted and remain the standard method of reporting tumour response to treatment. Recently, members of the National Cancer Institute (NCI), of the National Cancer Institute Canada (NCI Canada) and of the European Organization for Research and Treatment of Cancer (EORTC) have proposed a new set of tumour response criteria (Response Evaluation Criteria in Solid Tumours : RECIST) designed to replace existing WHO criteria[3].