RECIST 1.1 Overview
title: “RECIST 1.1 Overview” type: assessment category: recist/assessment tags: [recist, oncology, clinical-trials, solid-tumors, response-assessment] sources:
- file: “recist_eisenhauer_2009.pdf” page: “228-247”
- file: “recist_schwartz_2016.pdf” page: “132-137”
- file: “ajr_vandenabbeele_2012.pdf” page: “entire” date_created: 2025-04-15 date_modified: 2025-04-15 confidence: high anki_deck: “Radiology::RECIST” weak_area: false
Definition
RECIST 1.1 (Response Evaluation Criteria in Solid Tumors, version 1.1) is the standardized system for assessing tumor response to treatment in solid malignancies using anatomical imaging. Published by the EORTC in 2009 as a revision of RECIST 1.0 (2000), which replaced the WHO bidimensional criteria (1981).
The core principle: change in tumor size — measured as the sum of longest diameters on CT — serves as a validated surrogate endpoint for clinical benefit in clinical trials and increasingly in routine care.
The Four Response Categories
| Category | Definition |
|---|---|
| CR (Complete Response) | Disappearance of all target lesions + all non-target lesions + nodes <10mm short axis |
| PR (Partial Response) | ≥30% decrease in sum of diameters of target lesions vs. baseline |
| SD (Stable Disease) | Neither sufficient shrinkage for PR nor sufficient increase for PD |
| PD (Progressive Disease) | ≥20% increase in sum of diameters (vs. nadir) AND ≥5mm absolute increase; OR unequivocal progression of non-targets; OR any new lesion |
Measurable vs Non-Measurable Disease
At baseline, all lesions are classified as either measurable or non-measurable:
- Measurable: Solid lesion ≥10mm longest diameter on CT (≤5mm slice); nodal lesion ≥15mm short axis
- Non-measurable: Lesions <10mm, nodes 10–14mm short axis, truly non-measurable disease (bone-only, leptomeningeal, ascites, lymphangitic spread)
See Measurable Disease for full criteria.
Target and Non-Target Lesions
From measurable lesions, up to 5 target lesions (max 2 per organ) are selected and tracked as the sum of diameters. All remaining disease becomes non-target lesions and is followed qualitatively.
See Target Lesions and Non-target Lesions.
The Master Overall Response Table
Overall response integrates three independent assessments:
- Target lesion response (CR/PR/SD/PD)
- Non-target lesion response (CR/non-CR non-PD/unequivocal progression)
- New lesions (present or absent)
| Target | Non-Target | New Lesions | Overall |
|---|---|---|---|
| CR | CR | No | CR |
| CR | Non-CR/non-PD | No | PR |
| PR | Any (non-PD) | No | PR |
| SD | Non-PD | No | SD |
| PD | Any | Any | PD |
| Any | PD | Any | PD |
| Any | Any | Yes | PD |
The Override Rule
Any new lesion — regardless of target and non-target response — triggers overall PD. This is non-negotiable.
The Role of FDG-PET
FDG-PET is supplementary in RECIST 1.1. It is used to detect new lesions but does not measure existing target lesions.
- Baseline PET positive → new PET focus at follow-up → new lesion = PD
- Baseline PET negative → new PET focus at follow-up → PD
- No baseline PET → new PET focus → confirm on CT before declaring PD
See New Lesions for the complete PET decision rules.
Clinical Endpoints Derived from RECIST
| Endpoint | Definition |
|---|---|
| ORR (Objective Response Rate) | CR + PR ÷ all evaluable patients |
| PFS (Progression-Free Survival) | Time from randomization to PD or death |
| TTP (Time to Progression) | Time from randomization to PD (death censored) |
| BOR (Best Overall Response) | Best confirmed response from start of treatment to progression |
| Duration of Response | Time from first CR/PR documentation to PD |
Alternative Criteria
RECIST 1.1 is the reference standard for solid tumors. Specific tumor types and therapies require modified criteria:
- Choi criteria — GIST treated with imatinib (incorporates density change)
- iRECIST — Immunotherapy (introduces unconfirmed PD for pseudoprogression)
- mRECIST — HCC treated with locoregional therapies (targets arterial enhancement only)
- Lugano/Cheson — Lymphoma (incorporates FDG-PET, Deauville scoring)
See Alternative Response Criteria for full comparison.
Baseline Requirements
- Baseline scan must be performed within 4 weeks of treatment initiation
- CT with ≤5mm contiguous slices is the standard modality
- MRI is an acceptable alternative
- Ultrasound, chest X-ray, and endoscopy cannot be used for target lesion measurement
- Tumor markers alone cannot assess response (but support CR for non-target disease if normalized)
Follow-up Frequency
- Phase II trials: every 6–8 weeks, timed to end of treatment cycle
- Protocol-specific for phase III
- Evaluation interval is adapted to tumor biology and treatment schedule
Key Threshold Reminders
- 10mm: minimum longest diameter for measurable solid lesions
- 15mm short axis: minimum for measurably pathological lymph nodes
- 10mm short axis: threshold for “normal” node — below this, node not recorded
- 30% decrease: PR threshold (calculated vs. baseline sum)
- 20% increase + 5mm absolute: PD threshold (calculated vs. nadir)
- 4 weeks: minimum confirmation interval for CR/PR in non-randomized trials
- 6 weeks: minimum timepoint to qualify for SD as BOR