New guidelines to evaluate the response to treatment in solid Tumors

Anticancer cytotoxic agents go through a process by which their antitumor a ctivity-on the basis of the amount of tumor shrinkage they could generate-h as been investigated. In the late 1970s, the International Union Against Ca ncer and the World Health Organization introduced specific criteria for the codification of tumor response evaluation. In 1994, several organizations involved in clinical research combined forces to tackle the review of these criteria on the basis of the experience and knowledge acquired since then. After several gears of intensive discussions, a new set of guidelines is r eady that will supersede the former criteria. In parallel to this initiativ e, one of the participating groups developed a model by which response rate s could be derived from unidimensional measurement of tumor lesions instead of the usual bidimensional approach. This new concept has been largely val idated by the Response Evaluation Criteria in Solid Tumors Group and integr ated into the present guidelines. This special article also provides some p hilosophic background to clarify the various purposes of response evaluatio n. It proposes a model by which a combined assessment of all existing lesio ns, characterized by target lesions (to be measured) and nontarget lesions, is used to extrapolate an overall response to treatment. Methods of assess ing tumor lesions are better codified, briefly within the guidelines and in more detail in Appendix I. All other aspects of response evaluation have b een discussed, reviewed, and amended whenever appropriate.