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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 RECIST Guidelines • 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 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 Limitations of RECIST guidelines • Tumor morphology – Confluent, Irregular borders – Unusual configuration; Circumferential (eg. mesothelioma) – Lesion length > 1.5-2 times lesion width • Discordant results due to RECIST technique – Uni-dimensional measurement – Shape changes may confound results Lesion Confluence and Relationship to Normal Anatomical Structures Unusual Lesion Configuration Lesion Morphology: Mesothelioma Limitations of RECIST guidelines • Non-spherical, asymmetric tumor growth • Tumor size: Sub-centimeter tumors • Choosing representative tumor burden – Problematic when tumor burden is substantial – Differential tumor response Differential tumor behavior Pre Post Limitations of RECIST guidelines • 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 Differential tumor behavior Change in Tumor Form: From Solid to Non-Solid Limitations of RECIST guidelines • 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 Non-Drug treatment of tumors: Response criteria? Imaging Pitfalls: Scanning & Visualization Techniques Future? WHO-Bidimensional RECIST-Unidimensional Volumetric