Measuring response in solid tumors: Comparison of RECIST and WHO response criteria

Background: Objective tumor response is a common endpoint in daily practice as well as in clinical trials to evaluate the efficacy of anti-cancer agents. Traditionally, the standard World Health Organization (WHO) criteria has been adopted in these contexts. However, the recent development of new classes of anti-cancer agents and progress in imaging technology have required new methodology to evaluate response to treatment. Recently, the Response Evaluation Criteria in Solid Tumors Group (RECIST) proposed new guidelines using unidimensional measurement. Theoretically, the simple sum of the maximum diameters of individual tumors is more linearly related to cell kill than is the sum of the bidimensional products. To validate these new guidelines, we have compared the standard WHO response criteria with the new RECIST guidelines in the same patient population. Methods: Data from 79 patients enrolled in eight prospective phase II studies at Samsung Medical Center were retrospectively re-analyzed to determine the concordance between the two response criteria. The two response criteria were applied separately, and the results were compared using the kappa statistic to test concordance for overall response rate. Results: The overall response rate according to the WHO criteria was 31.6%. Using the RECIST criteria, nine patients were reclassified and the overall response rate was 30.4%. There was excellent agreement between the unidimensional and bidimensional criteria in 23 of 25 responses (92%). The kappa statistic for concordance for overall response was 0.91. Conclusions: We conclude that the new RECIST guidelines are comparable to the old response criteria in evaluating response in solid tumors. Moreover, the new guidelines are just as simple and reproducible in the measurement of response in daily practice as they are in clinical trials.