Response Evaluation Criteria in Solid Tumors (RECIST) provides a standardized framework for assessing how solid tumors respond to cancer treatments. It offers an objective way to measure changes in tumor burden. RECIST was initially introduced in 2000 and later revised in 2009 to refine its criteria. It provides a consistent method to evaluate therapy effectiveness in oncology.
Purpose and Importance of RECIST
RECIST was developed to provide a uniform method to evaluate tumor response across various clinical trials and treatment centers. Previously, varied measurement approaches hindered comparison of study results. The criteria standardize tumor response assessment, aiding comparison of new therapies.
This standardization facilitates communication among oncologists and researchers, offering a common language for discussing treatment outcomes. This consistency supports evidence-based treatment decisions and accelerates the development of new anti-cancer drugs. By providing a quantifiable measure of treatment efficacy, RECIST helps determine if a new therapy is beneficial.
How RECIST is Applied
RECIST categorizes tumors into “target lesions” (measurable) and “non-target lesions” (non-measurable). Target lesions are those that can be accurately measured in at least one dimension, with a longest diameter of 10 mm or more via spiral CT scan. These are selected for repeated measurements.
For target lesions, the longest diameter is measured, and a baseline sum of these diameters is calculated at the beginning of treatment. This baseline sum serves as the reference for subsequent evaluations. Pathological lymph nodes are also considered measurable if their short axis is 15 mm or more.
Non-target lesions are recorded at baseline, but their measurements are not required; only their presence or absence is noted during follow-up. Based on changes in target lesions and the status of non-target lesions, the response is classified into four main categories:
Complete Response (CR): Signifies the disappearance of all target and non-target lesions, with any pathological lymph nodes shrinking to less than 10 mm in short axis.
Partial Response (PR): Occurs when there is at least a 30% decrease in the sum of the longest diameters of target lesions compared to the baseline sum, with no progression of non-target lesions.
Stable Disease (SD): Defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for Progressive Disease (PD), relative to the smallest sum of diameters recorded since treatment began.
Progressive Disease (PD): Identified by at least a 20% increase in the sum of the longest diameters of target lesions, with a minimum absolute increase of 5 mm, or the appearance of one or more new lesions.
Interpreting RECIST Results for Patients
RECIST classifications provide oncologists objective information on how a patient’s tumor responds to treatment. A Complete Response or Partial Response indicates that the treatment is shrinking the tumor, suggesting effective therapy and often supporting continuation of the current regimen.
Stable Disease suggests that the tumor is not growing significantly, and not shrinking enough for a partial response. In such cases, the oncologist might decide to continue the current treatment, especially if the patient is tolerating it well and experiencing symptom control. However, they may also consider other options if the patient’s condition is not improving.
Progressive Disease signifies that the tumor is growing or new lesions have appeared, indicating the current treatment may not be effective. When this occurs, oncologists discuss modifying or stopping the current treatment and exploring alternative therapies. This decision is made in consultation with the patient.
RECIST results are one piece of information used in treatment planning. Oncologists also consider other factors, such as the patient’s overall well-being, symptoms, quality of life, and the presence of any treatment side effects. These discussions help determine the most appropriate next steps in their care.