Introduction
RECIST criteria provide standardized rules for measuring tumor response using size based metrics on CT and MRI and are widely used in clinical trials. Functional and molecular imaging add complementary information about metabolic and physiologic changes that precede size changes. Newer criteria incorporate PET metrics and volumetric assessments for more sensitive response evaluation.
RECIST and Modifications
RECIST defines measurable lesions and thresholds for partial response stable disease and progression and has been adapted for specific tumor types and therapies. Limitations include inability to capture pseudoprogression and immune related response patterns. Modified criteria and immune response guidelines address these challenges.
Functional and Molecular Imaging
PET based metrics such as SUV changes and dynamic contrast MRI parameters provide early indicators of treatment effect. Radiomics and quantitative imaging biomarkers may predict response and resistance patterns. Multimodality assessment improves decision making in complex therapeutic contexts.
Clinical Implementation
Standardized acquisition and timing relative to therapy are essential for reliable response assessment. Multidisciplinary tumor boards integrate imaging findings with clinical and laboratory data to guide management. Prospective validation of novel imaging endpoints supports regulatory acceptance and clinical use.