New guidelines to evaluate the response to treatment in solid tumors

Anticancer agents go through a process by which their antitumor activity, o n the basis of the amount of tumour shrinkage they generate, has been inves tigated. In the late 1970s, the International Union Against Cancer and the World Health Organization (WHO) introduced specific criteria for the codifi cation of tumor response evaluation. In 1994, several organizations involve d in clinical cancer research joined together to undertake the review of th e basis of their experience and knowledge. After several years of intensive discussions, new guidelines are ready and will replace the previous WHO cr iteria. In parallel to this initiative, one of the participating groups dev eloped a model by which response rates could be derived from unidimensional measurement of tumor lesions instead of the usual bidimensional approach. This new concept has been largely validated by the Response Evaluation Crit eria in Solid Tumors (Recist) Group and integrated into the present guideli nes. This special article provides some philosophic background to clarify t he various purposes of response evaluation. It proposes a model by which a combined assessment of all existing lesions, characterized by target lesion (to be measured) and nontarget lesions, is used to extrapolate an overall response to treatment. Methods of assessing tumor lesions are better codifi ed. All other aspects of response evaluation have been discussed, reviewed, and amended whenever suitable.