recist criteria calculator

What is RECIST and why it matters

RECIST (Response Evaluation Criteria in Solid Tumors) is a standardized framework used in oncology to assess how tumors respond to treatment on imaging. By applying consistent rules, RECIST helps clinicians and researchers compare outcomes across time, across patients, and across clinical trials.

In RECIST 1.1, selected measurable lesions are tracked over time as target lesions. Their diameters are added to produce a sum, and that sum is compared with baseline and nadir values. The resulting category usually falls into one of four responses: Complete Response (CR), Partial Response (PR), Stable Disease (SD), or Progressive Disease (PD).

RECIST 1.1 target-lesion thresholds

• CR (Complete Response): Disappearance of all target lesions (and pathological nodes reduce to <10 mm short axis).
• PR (Partial Response): At least a 30% decrease in sum of diameters relative to baseline.
• PD (Progressive Disease): At least a 20% increase from nadir and at least a 5 mm absolute increase.
• SD (Stable Disease): Does not meet criteria for CR, PR, or PD.

RECIST also considers new lesions and non-target progression. In practical terms, either of those findings generally drives classification toward PD, even if target-lesion measurements alone look improved.

How to use this calculator

1. Enter the baseline sum from the initial measurable target lesions.
2. Enter the nadir sum, which is the smallest prior sum recorded during therapy (optional; blank defaults to baseline).
3. Enter the current sum from the latest scan.
4. Check boxes for new lesions, non-target progression, and CR-specific findings when present.
5. Click Calculate RECIST Response to view category and supporting calculations.

Quick worked example

Suppose baseline is 100 mm, nadir is 70 mm, and current is 86 mm:

• Change from baseline = -14% (not enough for PR)
• Change from nadir = +22.9%, absolute increase = +16 mm (meets PD threshold)
• Result = PD (if no contradictory data and no CR conditions)

Important clinical nuances

1) This is a support tool, not a diagnosis engine

Treatment decisions require context: disease biology, symptom burden, treatment toxicity, imaging quality, and physician judgment. A numerical category should always be interpreted in the full clinical picture.

2) Lesion selection quality matters

RECIST depends on consistent target-lesion selection and measurement method. If measurement technique changes between scans, response categorization can be misleading.

3) Immunotherapy patterns can differ

Some patients on immunotherapy may show atypical response patterns. In those scenarios, immune-specific frameworks (for example iRECIST approaches) may be considered by the treating team.

Frequently asked questions

Do I always need the nadir?

For PD assessment, yes—it is the key comparator. If no lower prior value exists, baseline often serves as the initial reference.

Can a patient be PR and PD at the same time?

In practical reporting, no. RECIST classification follows hierarchical logic. New lesions or unequivocal non-target progression typically override PR-like target changes and result in PD.

What if current sum is zero?

A zero target sum alone does not automatically mean CR unless CR conditions are satisfied (including nodal criteria). This calculator includes checkboxes so you can explicitly confirm these findings.