The newly introduced Response Evaluation Criteria in Solid Tumors (RECIST), which relies on a single largest dimension of tumor rather than on the product of perpendicular diameters World Health Organisation (WHO) is intended to simplify the assessment of tumor response.
Purpose: Is to evaluate the performance and validity of the RECIST compared to the WHO criteria.
Design: Thirty-four consecutive patients with bidimensionally measurable malignant pleural mesothelioma (MPM) were evaluated prospectively.
Results: In 27% (9/34) a discrepancy was found between the WHO and RECIST response evaluation 9% (3/34) concerned best responses and 18% (6/34) objective confirmed responses. In 24% (8/34) disease progression was missed by RECIST. The percentage of patients in whom one or more discordance's between WHO and RECIST were detected was 47, 88% due to underscoring by RECIST. In a subgroup of 24 MPM patients with bidimensionally measurable pleural lesions only, the discrepancy rate was 29%, always due to underscoring by RECIST. However, when in the same subgroup the modified RECIST response evaluation was used the discrepancy rate was 21% and in all cases due to underscoring by WHO.
Conclusion: For MPM bidimensional WHO response evaluation cannot automatically be replaced by RECIST because MPM has a non-spherical growth pattern. Our recommendation is to use the WHO criteria for bidimensional measurable lesions, RECIST for unidimensional measurable lesions and a modified RECIST response evaluation, in which the short axis perpendicular to the chest wall is used, for thickened pleural rind disease, according to the method used in the recently completed pemetrexed (Alimta) trial for MPM.