RECIST 1.1 Response Evaluation Criteria in Solid Tumours v1.1

{
  "categories": [
    {
      "outcome_code": "CR",
      "label": "complete_response",
      "target_state": "all_target_lesions_disappeared_and_all_pathologic_nodes_below_10_mm_short_axis"
    },
    {
      "outcome_code": "PR",
      "label": "partial_response",
      "target_state": "sum_of_target_diameters_decreased_at_least_30_percent_from_baseline"
    },
    {
      "outcome_code": "SD",
      "label": "stable_disease",
      "target_state": "neither_PR_from_baseline_nor_PD_from_nadir"
    },
    {
      "outcome_code": "PD",
      "label": "progressive_disease",
      "target_state": "sum_increased_at_least_20_percent_from_nadir_and_at_least_5_mm_absolute_or_other_progression_override"
    }
  ],
  "applicability": {
    "use_for": "Standardized anatomic tumor-burden and response assessment in solid-tumor clinical trials using reproducible serial CT or protocol-appropriate MRI.",
    "classification_unit": "one_patient_at_one_protocol_defined_timepoint_with_target_nontarget_and_new_lesion_synthesis",
    "required_inputs": [
      "solid_tumor_and_trial_or_clinical_context",
      "treatment_start_date",
      "baseline_imaging_within_4_weeks_before_treatment",
      "fixed_target_lesion_set",
      "baseline_sum_of_diameters",
      "current_sum_of_diameters",
      "smallest_on_study_sum",
      "nontarget_status",
      "new_lesion_status",
      "technical_evaluability"
    ],
    "outside_scope": [
      "malignant_lymphoma_when_Lugano_is_required",
      "adult_glioma_when_RANO_is_required",
      "metabolic_response_as_a_substitute_for_anatomic_RECIST",
      "immune_confirmation_rules_unless_iRECIST_is_explicit",
      "therapy_selection_from_response_code_alone"
    ]
  },
  "baseline_and_technical_gate": {
    "timing": "Perform baseline evaluation as close as possible to treatment start and no more than 4 weeks before it.",
    "consistency": "Use the same assessment method, modality, contrast phase, acquisition technique, reconstruction and anatomic coverage at baseline and follow-up whenever possible.",
    "preferred_cross_sectional_method": "CT is the principal reproducible method; MRI is acceptable in appropriate settings. The same lesion should not switch between CT and MRI measurements without a protocol-valid comparable baseline.",
    "slice_rule": "With CT or MRI slices no thicker than 5 mm, the usual nonnodal minimum is 10 mm. If slice thickness exceeds 5 mm, both baseline measurability and interpretation must use a minimum longest diameter of at least twice the actual slice thickness and account for gaps.",
    "ultrasound_rule": "Do not use ultrasound lesion dimensions for RECIST objective-response measurement because serial reproducibility and whole-lesion review are insufficient.",
    "failure_rule": "If a required target lesion, site or technique is not evaluable, do not remove it from the follow-up sum while retaining it at baseline. Return NE unless a protocol review can prove the missing contribution cannot change the result."
  },
  "baseline_measurability": {
    "nonnodal_target": "Longest diameter at least 10 mm on CT or MRI acquired at 5 mm or thinner slices, with a reproducibly measurable margin.",
    "lymph_node_target": "Short axis at least 15 mm on CT; always measure and follow the short axis.",
    "lymph_node_nontarget": "Pathologic node with short axis at least 10 mm but below 15 mm.",
    "normal_node": "Short axis below 10 mm is nonpathologic for RECIST and is neither target nor nontarget disease.",
    "nonmeasurable_examples": [
      "nonnodal_lesion_below_10_mm",
      "node_10_to_below_15_mm_short_axis",
      "leptomeningeal_disease",
      "ascites",
      "pleural_or_pericardial_effusion",
      "inflammatory_breast_disease",
      "lymphangitic_skin_or_lung_disease",
      "nonreproducible_organomegaly"
    ],
    "bone_lesion_rule": "A lytic or mixed bone lesion is measurable only through a reproducible soft-tissue component meeting the size rule. Blastic disease and bone-scan, PET or plain-film abnormalities alone are nonmeasurable.",
    "cystic_lesion_rule": "A malignant cystic metastasis can be measurable if it meets the size rule, but a noncystic measurable lesion is preferred as a target when available; a simple cyst is not tumor.",
    "prior_local_therapy_rule": "A lesion in a previously irradiated or locally treated region is generally nonmeasurable unless progression has been demonstrated and the protocol prespecifies its use."
  },
  "target_selection_and_measurement_model": {
    "count_rule": "Select no more than five measurable target lesions total and no more than two per organ, representative of involved organs.",
    "paired_organ_rule": "Lungs, kidneys, ovaries and all nodal chains each count as one organ for the two-target-per-organ limit.",
    "selection_rule": "Prefer the largest lesions that remain reproducibly measurable. A slightly smaller reproducible lesion is preferable to an irregular or poorly delimited largest lesion.",
    "fixed_set_rule": "Keep the baseline target set throughout follow-up. Do not replace a responding target with a newly conspicuous lesion or silently drop an unevaluable target.",
    "diameter_rule": "Measure the longest diameter of each nonnodal target and the short axis of each nodal target in millimeters, allowing the measurement vector to change with lesion shape.",
    "sum_rule": "Add nonnodal longest diameters and nodal short axes into one target sum. Store every lesion measurement, the sum, the baseline sum and the dated smallest valid sum on study.",
    "nontarget_rule": "Record all other disease at baseline and follow qualitatively as absent, present or unequivocally progressed; do not calculate an invented diameter sum for the nontarget group."
  },
  "follow_up_measurement_rules": {
    "below_baseline_minimum": "Measurability is determined at baseline. Continue recording the actual target dimension even after it falls below 10 mm.",
    "too_small_to_measure": "If a nonnodal target is visibly present but too small for a reliable dimension, record the protocol default 5 mm. Record 0 mm only when it has truly disappeared.",
    "nodal_follow_up": "Continue the actual nodal short-axis measurement even below 10 mm; a node below 10 mm is normal for CR even though the target sum may remain above zero.",
    "coalesced_lesions": "If lesions remain separable, measure each. If fully coalesced, measure the longest diameter of the confluent mass; apply the corresponding short-axis rule to a nodal conglomerate.",
    "split_lesion": "If one target separates into distinct lesions, measure the longest diameter of each resulting lesion and add them to the sum."
  },
  "target_response_algorithm": [
    {
      "priority": 1,
      "if": "all_target_lesions_disappeared_AND_every_pathologic_target_or_nontarget_node_short_axis_below_10_mm",
      "output_code": "CR"
    },
    {
      "priority": 2,
      "if": "current_sum_at_least_30_percent_below_baseline_sum",
      "output_code": "PR"
    },
    {
      "priority": 3,
      "if": "current_sum_at_least_20_percent_above_smallest_on_study_sum_AND_absolute_increase_at_least_5_mm",
      "output_code": "PD"
    },
    {
      "priority": 4,
      "if": "neither_PR_relative_to_baseline_nor_PD_relative_to_smallest_on_study_sum",
      "output_code": "SD"
    }
  ],
  "reference_and_boolean_rules": {
    "PR_reference": "PR always uses the baseline target sum. Both the direction and the 30-percent threshold must be retained.",
    "PD_reference": "PD uses the smallest valid target sum on study, including baseline if it is the smallest.",
    "PD_AND_rule": "Target-sum PD requires both at least 20 percent relative growth and at least 5 mm absolute growth. Meeting only one condition does not establish target PD.",
    "SD_dual_reference": "SD means insufficient shrinkage from baseline for PR and insufficient growth from nadir for PD; using one reference for both silently changes RECIST 1.1.",
    "ongoing_PR_rule": "After PR is established, a later target sum remains PR unless PD criteria are met; it need not retain a 30-percent reduction at every later visit when assessed against nadir under committee clarification."
  },
  "nontarget_and_new_lesion_rules": {
    "nontarget_CR": "All nontarget lesions disappear, tumor markers required by the protocol normalize, and every pathologic node is below 10 mm short axis.",
    "nontarget_non_CR_non_PD": "One or more nontarget lesions persist without unequivocal progression. Do not relabel this qualitative state as nontarget SD.",
    "nontarget_PD": "Unequivocal progression must represent substantial overall worsening sufficient to alter the global disease state. A modest increase in one nontarget lesion usually cannot override target PR or SD.",
    "new_lesion_PD": "One or more unequivocally new malignant lesions establish PD and do not need to meet baseline target measurability thresholds.",
    "equivocal_new_lesion": "If a suspected new lesion is too small or technically uncertain, continue protocol-appropriate follow-up. If confirmed, backdate PD to the first suspicious scan; if it resolves, treat it as artifact or benign change.",
    "flare_guard": "Exclude technique change, infection, treatment effect, healing bone flare, necrotic transformation and a previously unscanned site before declaring a focus newly malignant; disease discovered in a newly imaged anatomic site still counts as new disease when credible.",
    "FDG_PET_boundary": "FDG PET is complementary for possible new disease. It does not override a CT or MRI target-sum result unless the protocol-defined anatomic new-lesion algorithm is satisfied."
  },
  "overall_response_synthesis": [
    {
      "target": "CR",
      "nontarget": "CR",
      "new_lesion": "absent",
      "output_code": "CR"
    },
    {
      "target": "CR",
      "nontarget": "non_CR_non_PD_or_not_fully_evaluated",
      "new_lesion": "absent",
      "output_code": "PR"
    },
    {
      "target": "PR",
      "nontarget": "non_PD_or_not_fully_evaluated",
      "new_lesion": "absent",
      "output_code": "PR"
    },
    {
      "target": "SD",
      "nontarget": "non_PD_or_not_fully_evaluated",
      "new_lesion": "absent",
      "output_code": "SD"
    },
    {
      "target": "PD",
      "nontarget": "any",
      "new_lesion": "present_or_absent",
      "output_code": "PD"
    },
    {
      "target": "any",
      "nontarget": "unequivocal_PD",
      "new_lesion": "present_or_absent",
      "output_code": "PD"
    },
    {
      "target": "any",
      "nontarget": "any",
      "new_lesion": "present",
      "output_code": "PD"
    },
    {
      "target": "not_fully_evaluated",
      "nontarget": "non_PD",
      "new_lesion": "absent",
      "output": "NE"
    }
  ],
  "confirmation_and_reappearance_rules": {
    "response_confirmation": "Confirm CR or PR at least 4 weeks later only in nonrandomized trials where objective response is the primary endpoint. Randomized studies do not automatically require this confirmation.",
    "preliminary_response": "When confirmation is protocol-required, retain the initial CR or PR as unconfirmed until the confirmatory examination; do not erase the first-response date.",
    "target_reappearance_after_PR_or_SD": "A previously invisible target that reappears after overall PR or SD is added back into the target sum and is PD only if the full sum meets PD; it is not automatically a new lesion.",
    "reappearance_after_confirmed_CR": "Reappearance of malignant disease after a valid overall CR establishes PD, with special caution for nodes near 10 mm and for an earlier false CR."
  },
  "evaluability_and_abstention": {
    "NE_state": "Return not evaluable when required lesions or sites are missing, technique change destroys comparability, or incomplete measurements could change the category.",
    "no_measurable_baseline": "Patients with only nontarget disease can be evaluated for progression endpoints but cannot receive target-lesion PR or SD; use the official nontarget-only states and overall table.",
    "missing_target_rule": "Never include a target at baseline and omit it from follow-up solely because it became hard to measure; that creates false shrinkage.",
    "ambiguity_rule": "Preserve an equivocal progression state and the required follow-up rather than converting measurement uncertainty into PD."
  },
  "variant_boundaries": {
    "RECIST_1_1": "Conventional anatomic response using fixed unidimensional target sums plus qualitative nontarget and new-lesion review.",
    "iRECIST": "Immunotherapy trials may use iUPD and iCPD confirmation states. Do not apply them to conventional RECIST 1.1 unless the protocol explicitly specifies iRECIST.",
    "mRECIST_and_Choi": "mRECIST for HCC and Choi for GIST use viable enhancement or attenuation rules. Calculate them separately and never overwrite the conventional RECIST result.",
    "PERCIST": "PERCIST evaluates FDG metabolism with SULpeak and different technical gates. A metabolic response cannot be inserted into the RECIST diameter algorithm.",
    "disease_specific_criteria": "Use protocol-specified RANO, Lugano or other validated disease-specific criteria when conventional RECIST is inappropriate."
  },
  "management_and_risk_context": {
    "management_rule": "RECIST 1.1 standardizes trial endpoints and is not intended by itself to decide continuation or change of therapy except when the treating oncologist and protocol use it in context.",
    "progression_rule": "A confirmed PD mechanism should be communicated with the target sum, nontarget finding or new lesion that caused it; an agent must not autonomously stop therapy.",
    "risk_rule": "CR, PR, SD and PD do not provide individualized survival, cure or resistance probabilities. Tumor biology, regimen, symptoms, toxicity and time-to-event outcomes remain separate."
  },
  "output_contract": [
    "RECIST_1_1_and_any_named_disease_specific_or_immune_variant",
    "baseline_current_and_nadir_dates",
    "modality_protocol_slice_thickness_contrast_and_evaluability",
    "fixed_target_lesions_with_site_nonnodal_long_axis_or_nodal_short_axis",
    "baseline_current_and_smallest_on_study_sums",
    "percent_and_absolute_change_with_correct_reference",
    "nontarget_absent_present_or_unequivocal_progression",
    "new_lesions_and_equivocal_confirmation_status",
    "CR_PR_SD_PD_or_NE_with_trigger",
    "response_confirmation_requirement_and_status",
    "no_autonomous_treatment_or_prognostic_claim"
  ],
  "missing_input_behavior": [
    "If baseline target identity or measurements are missing, do not reconstruct them from a later scan or model memory.",
    "If the smallest on-study sum is unknown, do not call target PD from growth relative only to the immediately prior scan.",
    "If slice thickness or technique makes baseline measurability uncertain, return the rule and request protocol adjudication rather than rounding a lesion into eligibility.",
    "If a required target or site is unevaluable, return NE unless formal review proves the missing value cannot change the result.",
    "If a new focus is equivocal, preserve suspicion and the planned confirmation rather than finalizing PD.",
    "If only nonmeasurable disease exists, use the nontarget-only response states instead of inventing target SD or PR."
  ],
  "interpretation_limits": [
    "RECIST was developed primarily for clinical-trial response and progression endpoints; everyday treatment decisions require broader clinical judgment.",
    "Unidimensional size can miss biologically important change in enhancement, attenuation, metabolism or infiltrative disease; use validated disease-specific criteria when required.",
    "Measurement error, irregular lesions, coalescence, slice differences and incomplete coverage can change threshold classification near boundaries."
  ],
  "supporting_sources": [
    {
      "role": "primary_guideline",
      "citation": "Eisenhauer et al. Eur J Cancer. 2009;45:228-247",
      "doi": "10.1016/j.ejca.2008.10.026"
    },
    {
      "role": "committee_clarification",
      "citation": "Schwartz et al. Eur J Cancer. 2016;62:132-137",
      "doi": "10.1016/j.ejca.2016.03.081",
      "pmcid": "PMC5737828"
    },
    {
      "role": "current_official_resource",
      "citation": "RECIST Working Group RECIST 1.1 guidance and questions",
      "url": "https://recist.eortc.org/recist-1-1/"
    }
  ],
  "source_locator": "Eisenhauer et al. 2009, DOI 10.1016/j.ejca.2008.10.026: sections 2-4.5, Tables 1-2, Appendices I-III for scope, measurability, target selection, response thresholds, overall synthesis, new lesions, confirmation and imaging; Schwartz et al. 2016, PMC5737828, RECIST 1.1 clarifications; official RECIST Working Group RECIST 1.1 page checked for current status and live questions."
}