Response Evaluation Criteria in Solid Tumors, widely known as RECIST, provides a standardized framework for evaluating how solid tumors respond to cancer treatments. This system offers a consistent method for assessing changes in tumor size, allowing for clear and comparable evaluations across different studies and clinical settings. It serves as a common language, ensuring that assessments of treatment outcomes are objective and reproducible.
Why RECIST Matters
RECIST creates a shared understanding among oncologists globally, fostering consistency in how treatment outcomes are assessed. This standardization is valuable in the development of new cancer drugs through clinical trials. Researchers can reliably compare the efficacy of different therapies, as all participating sites use the same criteria to measure tumor response.
For individual patient management, RECIST offers an objective way to track disease progression or regression. Doctors use these standardized measurements to determine if a current treatment regimen is working as expected. This consistent evaluation helps guide decisions about continuing, modifying, or discontinuing a particular therapy.
How Tumors Are Measured
RECIST evaluations primarily rely on medical imaging techniques, such as computed tomography (CT) scans or magnetic resonance imaging (MRI). These scans capture detailed images of tumors, allowing for precise measurements. Specific lesions are designated as “target lesions” for measurement. These are chosen because they are measurable and representative of the patient’s disease.
Other visible tumors or abnormalities that are not precisely measured are categorized as “non-target lesions.” While not quantitatively measured, these non-target lesions are still monitored for their presence or disappearance. Measurements of target lesions are taken at the beginning of treatment, known as baseline, and at predetermined intervals throughout the therapy. The sum of the longest diameters of all identified target lesions is then calculated and used as the primary metric for evaluating tumor response.
Understanding Response Categories
RECIST defines distinct classifications for how solid tumors respond to treatment, providing clear criteria for assessment. A “Complete Response” (CR) indicates the disappearance of all identified target lesions, with no evidence of any remaining disease. For a CR, any non-target lesions must also resolve, and there should be no new lesions detected.
A “Partial Response” (PR) is defined by a significant reduction in tumor size. Specifically, the sum of the longest diameters of target lesions must decrease by at least 30% compared to the baseline measurement. All non-target lesions must remain stable, and no new lesions should appear.
“Stable Disease” (SD) describes a situation where the tumor burden neither shrinks enough to qualify as a partial response nor grows sufficiently to indicate progression. For stable disease, the sum of the longest diameters of target lesions must not have decreased by 30% or more, nor increased by 20% or more, compared to the smallest sum on study.
“Progressive Disease” (PD) signifies that the cancer is growing or spreading. This category is met if the sum of the longest diameters of target lesions increases by at least 20% compared to the smallest sum measured during the study, and this increase must also represent an absolute increase of at least 5 millimeters. The appearance of any new lesion, even without a significant increase in existing target lesions, also qualifies as progressive disease.
Practical Considerations for Evaluation
While RECIST provides objective criteria, the interpretation of these measurements still requires careful clinical judgment from the treating oncologist. Factors such as the quality and consistency of the imaging scans, along with the expertise of the radiologist performing the measurements, can influence the accuracy of the evaluation. These elements contribute to the overall reliability of the RECIST assessment.
A RECIST response, while a valuable indicator, does not always perfectly align with a patient’s overall well-being or survival outcomes. For example, a patient categorized with stable disease might still experience improvements in symptoms or have a longer life expectancy. RECIST criteria are specifically designed for the evaluation of solid tumors and are not applicable to blood cancers, such as leukemia or lymphoma, which require different assessment methods.