Modeling of mesothelioma growth demonstrates weaknesses of current response criteria.

Applicability of the Response Evaluation Criteria in Solid Tumors (RECIST) to the geometry of mesothelioma has been recently investigated. A "modified RECIST" measurement technique developed for mesothelioma proposes measurement of tumor thickness rather than maximum diameter. This study evaluated the volumetric consistency of the RECIST response criteria as applied to the modified RECIST measurement technique. Geometric models were developed to simulate mesothelioma growth, and measurements of these models were calculated. Relationships between change in model measurements and corresponding change in model volume were derived and evaluated. Application of the RECIST response criteria to the typical spherical tumor model results in partial response (PR) classification based on a 66% volume decrease and progressive disease (PD) based on a 73% volume increase; for mesothelioma model thickness measurements, the RECIST criteria result in PR classification based on a 30% volume decrease and PD based on a 20% volume increase. Alternative response criteria for mesothelioma thickness measurement (-66% for PR, +74% for PD) achieve volumetric equivalence with the RECIST criteria for spherical tumor measurement. Application of the RECIST response criteria to mesothelioma thickness measurements yields PR and PD classifications based on smaller volume changes than for spherical tumors.