RECIST 1.1 — Tumour Response Assessment
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Response Evaluation Criteria in Solid Tumours (RECIST) is the internationally standardised framework used to define and measure tumour response to cancer treatment in clinical trials and oncology practice. First published in 2000 (RECIST 1.0) and updated to RECIST 1.1 in 2009, the criteria provide objective, reproducible definitions of tumour response categories — complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD) — based on changes in the measured sum of diameters of target tumour lesions on cross-sectional imaging (CT or MRI). RECIST standardisation was essential for enabling reliable comparison of treatment efficacy across different clinical trials and centres, replacing the subjective tumour response assessments that preceded it. RECIST 1.1 introduced important refinements over the original version: the maximum number of target lesions was reduced from 10 to 5 (and from 5 to 2 per organ), lymph node measurement was standardised using the short axis (≥15 mm for measurable; 10–14 mm for non-target; <10 mm for normal), and the definition of progressive disease was refined to require both a relative increase of 20% and an absolute increase of at least 5 mm in the sum of target lesion diameters, preventing progressive disease categorisation from minor percentage increases in patients with very small baseline lesions. Non-target lesions are assessed qualitatively (present, absent, or unequivocal progression) and new lesions automatically trigger a progressive disease classification. RECIST has become the global standard for oncology drug development, required by regulatory authorities including the FDA and EMA for drug approval submissions.
CR = disappearance of all target lesions (and all non-target lesions); PR = ≥30% decrease in sum of target lesion diameters; PD = ≥20% increase + ≥5 mm absolute increase in sum of target lesion diameters, OR new lesions; SD = neither CR/PR nor PD criteria met
- 1At baseline, identify measurable target lesions: up to 5 lesions total (maximum 2 per organ), selecting the largest lesions that can be accurately measured and reproducibly followed. Minimum size: ≥10 mm in longest diameter for non-nodal lesions (CT); ≥15 mm short axis for lymph nodes.
- 2Measure each target lesion at its longest unidimensional diameter on CT/MRI (short axis for lymph nodes). Sum all target lesion diameters to obtain the baseline sum of diameters (SoD).
- 3Identify non-target lesions: all other measurable lesions and non-measurable disease. These are followed qualitatively — documented as present, improved, or unequivocally progressed.
- 4At each response assessment imaging scan, re-measure all target lesions and calculate the new SoD. Compare with baseline SoD and the nadir SoD (smallest SoD recorded since treatment started).
- 5Classify response: CR = all target lesions disappeared (and short axis of any previously target lymph node reduced to <10 mm); PR = ≥30% decrease from baseline SoD; PD = ≥20% increase from nadir SoD plus an absolute increase of ≥5 mm, or any new lesions; SD = does not meet PR or PD criteria.
- 6Assess non-target lesions: unequivocal progression of non-target disease (even without target lesion progression) triggers a PD classification. New lesions (any new radiologically identified lesion) always trigger PD.
- 7Document the date of each assessment, which lesions are target vs. non-target, all measurements, the SoD, percentage change from baseline, and the overall response category (CR/PR/SD/PD).
PR — treatment is working; continue current regimen
A 35.3% reduction in the sum of target lesion diameters exceeds the 30% threshold for partial response. This is a favourable treatment outcome and typically supports continuation of the current regimen.
Progressive disease — treatment change required; evaluate new regimen options
Both the 20% relative threshold and the 5 mm absolute increase threshold are satisfied. PD is confirmed. The patient requires oncology review and consideration of next-line therapy.
New lesions always constitute PD under RECIST 1.1
Even when target lesions are stable or slightly improved, a new lesion (not present at baseline and confirmed on follow-up imaging) mandates PD classification. Equivocal new lesions should be confirmed on the next scan before classifying as PD.
CR — all measurable disease eradicated; typically confirmed on a second scan ≥4 weeks later
CR requires complete disappearance of all target and non-target lesions. Lymph node targets must have a short axis below 10 mm. CR requires confirmation on a second assessment at least 4 weeks later per RECIST 1.1.
Drug approval submissions: regulatory agencies (FDA, EMA, PMDA) require RECIST-based response assessment as the primary tumour endpoint in most solid tumour drug approval applications., representing an important application area for the Recist Criteria in professional and analytical contexts where accurate recist criteria calculations directly support informed decision-making, strategic planning, and performance optimization
Clinical trial primary endpoints: objective response rate (ORR = CR + PR proportion) and progression-free survival (time to first PD or death) are the most common RECIST-based trial endpoints., representing an important application area for the Recist Criteria in professional and analytical contexts where accurate recist criteria calculations directly support informed decision-making, strategic planning, and performance optimization
Oncology clinical practice: oncologists use RECIST assessments at every 2–3 cycle CT scan to determine whether to continue, modify, or switch systemic treatment., representing an important application area for the Recist Criteria in professional and analytical contexts where accurate recist criteria calculations directly support informed decision-making, strategic planning, and performance optimization
Radiological reporting: radiologists at specialist cancer centres provide standardised RECIST measurement reports for oncology multidisciplinary team meetings, ensuring consistent interpretation., representing an important application area for the Recist Criteria in professional and analytical contexts where accurate recist criteria calculations directly support informed decision-making, strategic planning, and performance optimization
Health technology assessment: RECIST-derived endpoints (ORR, PFS) are used by HTA bodies such as NICE and IQWiG as evidence of clinical efficacy when evaluating new oncology drugs for reimbursement., representing an important application area for the Recist Criteria in professional and analytical contexts where accurate recist criteria calculations directly support informed decision-making, strategic planning, and performance optimization
Pseudoprogression on immunotherapy
{'title': 'Pseudoprogression on immunotherapy', 'body': 'Immune checkpoint inhibitors can cause initial tumour size increase due to immune cell infiltration before true tumour regression begins. This pseudoprogression mimics PD on RECIST but may represent clinical benefit. Modified iRECIST criteria require confirmation of apparent PD on a subsequent scan (usually 4–8 weeks later) before definitively classifying progressive disease in patients who remain clinically stable.'}
Bone metastases measurement
{'title': 'Bone metastases measurement', 'body': 'Bone lesions are generally non-measurable under RECIST unless they have a soft-tissue component that can be measured by CT. Lytic lesions with measurable soft-tissue mass can be target lesions; purely sclerotic or blastic lesions are non-target. Whole-body MRI and PSMA-PET are alternative response assessment methods for bone-dominant metastatic prostate cancer.'}
Peritoneal carcinomatosis
In the Recist Criteria, this scenario requires additional caution when interpreting recist criteria results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when recist criteria calculations fall into non-standard territory.
Brain metastases
{'title': 'Brain metastases', 'body': 'Brain metastases can be target lesions under standard RECIST if they are measurable and contrast-enhancing on MRI. However, the Response Assessment in Neuro-Oncology (RANO) criteria are preferred for primary brain tumours and increasingly used for brain metastasis assessment because they account for steroid effects, peritumoral oedema, and pseudo-response from antiangiogenic therapy.'}
| Category | Definition | Abbreviation | Implication |
|---|---|---|---|
| Complete Response | Disappearance of all target and non-target lesions; lymph nodes <10 mm short axis | CR | Best possible response — confirm on scan ≥4 weeks later |
| Partial Response | ≥30% decrease in sum of target diameters from baseline | PR | Treatment working — continue current regimen |
| Stable Disease | Neither PR nor PD criteria met | SD | Disease controlled — continue treatment if tolerated |
| Progressive Disease | ≥20% increase from nadir sum AND ≥5 mm absolute increase; OR new lesion | PD | Treatment failure — switch to next-line therapy |
| Not Evaluable | Insufficient data for assessment (e.g., scan not performed, lesion obscured) | NE | Document reason; repeat assessment planned |
| Target lesions maximum | 5 total, ≤2 per organ | — | Select largest reproducibly measurable lesions at baseline |
| Lymph node threshold | Short axis ≥15 mm for target; <10 mm = normal | — | Short axis, not longest diameter, for nodes |
What is RECIST and why is it important?
RECIST (Response Evaluation Criteria in Solid Tumours) is the standard framework for measuring tumour response to cancer treatment on imaging. It enables objective, reproducible assessment across different trials and centres, allowing regulatory agencies to evaluate drug efficacy from phase II and III trial data submitted for drug approval. This is particularly important in the context of recist criteria calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise recist criteria computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the difference between RECIST 1.0 and RECIST 1.1?
RECIST 1.1 (2009) made three key refinements to the original 2000 version: (1) maximum target lesions reduced from 10 to 5 (2 per organ); (2) lymph node measurement standardised to short axis with a 15 mm eligibility threshold; (3) progressive disease now requires both ≥20% relative increase and ≥5 mm absolute increase from nadir to prevent false PD classification in patients with very small lesions.
How many target lesions can be selected under RECIST 1.1?
RECIST 1.1 allows a maximum of 5 target lesions in total, with no more than 2 target lesions per organ. Target lesions should be the largest measurable lesions that can be accurately followed on serial imaging. All remaining measurable and non-measurable lesions are classified as non-target lesions. This is particularly important in the context of recist criteria calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise recist criteria computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is stable disease (SD)?
Stable disease is defined as neither sufficient shrinkage to qualify as PR (≥30% decrease from baseline) nor sufficient growth to qualify as PD (≥20% increase plus ≥5 mm absolute increase from nadir). SD represents a response category between benefit (PR) and failure (PD) and is considered disease control when it is sustained.
Is RECIST used for immunotherapy assessment?
Standard RECIST has limitations with immunotherapy because some patients experience pseudoprogression — initial tumour growth (from immune infiltration) followed by tumour shrinkage. Modified criteria (iRECIST, irRC, imRECIST) have been developed to capture this phenomenon, requiring confirmation scans before declaring true PD in patients who appear to be progressing on immune checkpoint inhibitors.
What does a new lesion mean in RECIST?
Under RECIST 1.1, any new lesion identified on follow-up imaging that was not present at baseline automatically constitutes progressive disease (PD), regardless of what is happening with the pre-existing target lesions. If a new lesion is equivocal (e.g., too small to characterise reliably), the assessment is flagged and confirmed on the next scheduled scan.
Can RECIST be used for leukaemia and lymphoma?
Standard RECIST was designed for solid tumours. Lymphoma uses the Lugano Classification (based on FDG-PET and CT), and leukaemia uses bone marrow-based response criteria (e.g., blast percentage, MRD negativity). RECIST is not validated for these haematological malignancies. This is particularly important in the context of recist criteria calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise recist criteria computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the minimum detectable lesion size under RECIST 1.1?
Non-nodal target lesions must have a longest diameter of at least 10 mm on CT (or 20 mm by chest X-ray). Lymph node target lesions must have a short axis of at least 15 mm. Lesions smaller than these thresholds are classified as non-measurable (non-target) and assessed qualitatively. This is particularly important in the context of recist criteria calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise recist criteria computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
Pro Tip
Always use the same imaging modality, contrast protocol, and scan parameters at baseline and all subsequent assessments. Switching from CT to MRI or changing contrast timing between assessments introduces measurement variability that makes response assessment unreliable and can create apparent changes that reflect imaging differences rather than true tumour change.
Did you know?
RECIST was partly born out of frustration with the WHO tumour response criteria published in 1979, which used bidimensional tumour measurement (multiplying two perpendicular diameters). RECIST replaced this with unidimensional measurement, which is simpler, more reproducible, and has been shown to be equally predictive of survival outcomes while reducing inter-rater disagreement by approximately 50%.
References
- ›Eisenhauer EA et al. New response evaluation criteria in solid tumours: Revised RECIST guideline (version 1.1). Eur J Cancer 2009.
- ›Therasse P et al. New guidelines to evaluate the response to treatment in solid tumors (RECIST 1.0). J Natl Cancer Inst 2000.
- ›Seymour L et al. iRECIST: guidelines for response criteria for use in trials testing immunotherapeutics. Lancet Oncol 2017.
- ›EORTC RECIST Working Group — Official RECIST 1.1 Documentation
- ›MDCalc — RECIST Criteria for Tumor Response