Limitations of RECIST guidelines Srinivasa R Prasad MD Associate Professor, Radiology University of Texas Health Science Center at San Antonio

RECIST Guidelines Response Evaluation Criteria In Solid Tumors Assumes spherical growth of round / ovoid tumors Uni-dimensional measurement technique –Less cumbersome, Simple math Arbitrary number of measurable lesions –5/organ; 10/patient

Target lesions: >1cm (Helical); >2cm (Non-helical) Measurement on axial images Increase in the threshold for classifying response as disease progression Primary modality: CT scan RECIST Guidelines

Limitations of RECIST guidelines No criteria for non-solid tumors No toxicity criteria Lower rate of disease progression? Not applicable to Non-Cytotoxic drugs?

Change in Tumor Form: From Solid to Non-Solid

Tumor morphology –Confluent, Irregular borders –Unusual configuration; Circumferential (eg. mesothelioma) –Lesion length > times lesion width Discordant results due to RECIST technique –Uni-dimensional measurement –Shape changes may confound results Limitations of RECIST guidelines

Lesion Confluence and Relationship to Normal Anatomical Structures

Unusual Lesion Configuration

Lesion Morphology: Mesothelioma

Non-spherical, asymmetric tumor growth Tumor size: Sub-centimeter tumors Choosing representative tumor burden –Problematic when tumor burden is substantial –Differential tumor response Limitations of RECIST guidelines

Differential tumor behavior Pre Post

Discordant results due to RECIST technique –Unusual Tumor morphology Confluent tumors, Unusual growth pattern Lesion length > 2 times lesion width Lesions with irregular / infiltrative borders –Unpredictable Tumor Behavior Differential tumor shrinkage/growth Limitations of RECIST guidelines

Differential tumor behavior

Change in Tumor Form: From Solid to Non-Solid

Updated imaging technology not considered –Multiplanar capability –Automated tumor detection –3-D data acquisition: volumetric tumor measurement Limitations of RECIST guidelines

Criteria for tumors treated by Non-drugs? (eg: Radio-frequency ablation) Metabolic and physiological changes predate tumor size change Limitations of RECIST guidelines

Non-Drug treatment of tumors: Response criteria?

Imaging Pitfalls: Scanning & Visualization Techniques

Future? WHO-Bidimensional RECIST-Unidimensional Volumetric