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Oncologic Imaging
Demonstration data

RECIST 1.1 Response

Classifies target-lesion tumour response from baseline, nadir and current sums of longest diameters.

The Response Evaluation Criteria In Solid Tumours (RECIST 1.1) provide a standardised measure of tumour burden change using the sum of longest diameters of target lesions, enabling reproducible categorisation of therapeutic response.

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📐 Formula

CR / PR (≥30% ↓ from baseline) / PD (≥20% ↑ and ≥5 mm from nadir) / SD

When to Use

  • Assessing target-lesion response of solid tumours on serial cross-sectional imaging.
  • Oncology trial reporting and routine treatment-response follow-up.
  • Determining progression to trigger a change in management.

How It Works

  • Sum the longest diameters of target lesions (short axis for nodal disease) at each time point.
  • Percent change from baseline drives partial response; percent change from nadir drives progression.
  • Complete Response (CR): disappearance of all target lesions (current sum = 0).
  • Partial Response (PR): ≥30% decrease in sum relative to baseline.
  • Progressive Disease (PD): ≥20% increase relative to nadir AND ≥5 mm absolute increase.
  • Stable Disease (SD): neither sufficient shrinkage for PR nor sufficient increase for PD.

Interpreting the Result

  • CR and PR represent objective response; SD may still reflect clinical benefit.
  • PD requires both the 20% relative and the 5 mm absolute thresholds to avoid over-calling small nadir changes.
  • Non-target lesions and new lesions (assessed separately) can also define progression regardless of target-lesion sum.

Limitations & Pitfalls

  • Only reflects size change; does not capture necrosis, metabolic or functional response.
  • Anatomic criteria may under-represent response to immunotherapy (see iRECIST).
  • Measurement variability and lesion selection affect reproducibility.

References

  • Eisenhauer EA, Therasse P, Bogaerts J, et al. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer. 2009;45(2):228-247.

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.