Response Evaluation Criteria in Solid Tumors v1.1 (RECIST v1.1)

RECIST v1.1 (Response Evaluation Criteria in Solid Tumors, version 1.1) is the internationally accepted framework for objectively assessing tumor response to treatment in solid tumors by radiographic measurement. Published in 2009 by Eisenhauer et al., RECIST v1.1 superseded RECIST 1.0 with key updates: reducing the maximum number of target lesions from 10 to 5 (maximum 2 per organ), adding lymph node measurement criteria (short axis ≥15 mm for target, <10 mm for CR), and clarifying progressive disease rules. Response is categorized as Complete Response (CR), Partial Response (PR), Stable Disease (SD), or Progressive Disease (PD) based on the sum of diameters of target lesions at each time point relative to baseline and nadir. RECIST v1.1 is the standard for solid tumor registration trials; iRECIST, RANO, and PCWG criteria apply to immunotherapy and specific disease settings.

Response Criteria — RECIST v1.1 Criteria

• CR: Complete Response — Disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to <10 mm. All non-target lesions must have resolved and tumor marker levels must have normalized. Best possible response. Typically the primary or key secondary endpoint in curative-intent studies. In practice, a confirmatory scan at ≥4 weeks is required to document CR. CR of non-target lesions requires normalization of all tumor markers in addition to lesion disappearance.
• PR: Partial Response — At least a 30% decrease in the sum of diameters (SoD) of target lesions, taking as reference the baseline SoD. Non-target lesions must be Non-CR/Non-PD and no new lesions may be present. Indicates meaningful tumor shrinkage; often used to demonstrate single-arm efficacy in phase II trials and serves as a secondary endpoint in phase III trials. ORR (CR + PR) is the standard composite endpoint. Confirmatory assessment ≥4 weeks after initial PR is required per protocol.
• SD: Stable Disease — Neither sufficient shrinkage to qualify for PR (i.e., <30% decrease from baseline SoD) nor sufficient increase to qualify for PD (i.e., <20% increase from nadir SoD). The nadir SoD is used as the reference for PD criteria. Prolonged SD (typically ≥6 months) can indicate clinical benefit, particularly for cytostatic agents (e.g., CDK4/6 inhibitors, mTOR inhibitors). Disease control rate (DCR) = CR + PR + SD ≥X weeks. SD is not a sufficient endpoint for accelerated approval but is incorporated in DCR and PFS analyses.
• PD: Progressive Disease — At least a 20% relative increase in the SoD of target lesions from the nadir SoD, plus an absolute increase of at least 5 mm. OR the appearance of one or more new lesions. OR unequivocal progression of non-target lesions. Primary endpoint in many trials (event for PFS); triggers off-study evaluation in most trial protocols. The 5 mm absolute-increase requirement prevents false PD in patients with very small baseline tumor burden. New lesions must be unequivocal — borderline lesions should be tracked and confirmed at the next scan.
• Non-CR/Non-PD: Non-CR / Non-PD (Non-Target Lesions) — Persistence of one or more non-target lesion(s) and/or maintenance of tumor marker levels above normal limits, but no unequivocal progression of non-target lesions and no new lesions. This response category applies only to non-target lesion assessment. When target lesion response is CR but non-target lesions are Non-CR/Non-PD, the overall best response is PR (not CR) — full CR requires complete resolution of all lesions including non-target lesions and normalization of tumor markers.
• iUPD: Unconfirmed PD (iRECIST) — Immune-modified RECIST designation for apparent progressive disease at first post-baseline assessment that has not yet been confirmed at a subsequent scan ≥4 weeks later. Allows continuation of immunotherapy pending confirmation. Applicable in immunotherapy trials using iRECIST only. Pseudoprogression (immune-mediated tumor flare before response) occurs in 4–10% of patients on checkpoint inhibitors. Confirmation at the next scheduled scan converts iUPD to either confirmed PD (iCPD) or a response/stable category if the tumor subsequently shrinks.