recist calculator

This RECIST calculator helps estimate treatment response using RECIST 1.1 style thresholds based on target lesion measurements. Enter the baseline sum, current sum, and nadir sum (the lowest prior sum) to get a quick classification.

What is RECIST?

RECIST stands for Response Evaluation Criteria in Solid Tumors. It provides standardized rules for determining whether cancer burden has improved, worsened, or remained stable after treatment. The framework is widely used in oncology trials and clinical documentation because it creates a common language across institutions and studies.

Core RECIST response categories

• CR (Complete Response): Disappearance of all target lesions (and pathological nodes reduced to below 10 mm short axis).
• PR (Partial Response): At least a 30% decrease in the sum of target lesion diameters compared with baseline.
• SD (Stable Disease): Neither sufficient shrinkage for PR nor sufficient increase for PD.
• PD (Progressive Disease): At least a 20% increase versus nadir and an absolute increase of at least 5 mm, or appearance of new lesions.

How this calculator works

This tool focuses on the numerical RECIST thresholds for target lesions and includes key binary modifiers: new lesions, unequivocal non-target progression, and complete target lesion disappearance.

• Step 1: It checks for new lesions or unequivocal non-target progression (these indicate PD).
• Step 2: It checks complete disappearance criteria (CR).
• Step 3: It computes percent change from baseline and from nadir for PR/PD logic.
• Step 4: If PR and PD are not met, it returns SD.

Practical interpretation tips

1) Baseline and nadir are not interchangeable

PR is judged against baseline. PD (target lesion growth) is judged against nadir, the smallest recorded sum. That means a patient can still be below baseline yet be PD if they increase enough from nadir.

2) Absolute increase matters for PD

The 20% increase criterion alone is not enough for target-lesion PD. There must also be at least a 5 mm absolute increase. This avoids over-calling progression from tiny measurement fluctuations.

3) Imaging context remains essential

RECIST values should be interpreted alongside radiology review, lesion selection consistency, scan quality, and clinical context. A calculator is useful for consistency, but not a replacement for multidisciplinary judgment.

Worked example

Suppose baseline sum is 100 mm, nadir is 60 mm, and current sum is 74 mm:

• Change from baseline: -26% (not enough for PR).
• Change from nadir: +23.3%, absolute increase: +14 mm.
• Meets PD target-lesion criteria because increase from nadir is ≥20% and ≥5 mm absolute.

Even though the current burden is still lower than baseline, RECIST classification can be PD relative to nadir.

Limitations and disclaimer

This calculator is an educational aid and quick-check tool. It does not replace formal RECIST assessment, radiology reports, protocol-specific adjudication, or physician decision-making. Always verify against the exact trial protocol or institutional standard.