Non-target Lesions
title: “Non-target Lesions” type: descriptor category: recist/descriptor tags: [recist, non-target-lesions, qualitative-assessment] sources:
- file: “recist_eisenhauer_2009.pdf” page: “235-237” date_created: 2025-04-15 date_modified: 2025-04-15 confidence: high anki_deck: “Radiology::RECIST” weak_area: false
Definition
Non-target lesions encompass all disease that is not selected as a target lesion. They are followed qualitatively — assessed as present, absent, or unequivocally progressing — not measured numerically. Non-target lesions do not contribute to the sum of diameters.
What Qualifies as a Non-target Lesion?
Two categories:
- Measurable lesions not selected as targets — measurable but not chosen for the 5-target-limit
- Non-measurable disease — any disease that cannot be accurately measured (see Measurable Disease)
This includes: small nodes (10–14mm SAD), bone-only metastases, leptomeningeal disease, ascites, effusions, lymphangitic spread, cystic/necrotic lesions without solid components, and lesions in irradiated fields.
How Non-target Lesions Are Tracked
At each follow-up, non-target lesions are assigned one of four statuses:
| Status | Meaning |
|---|---|
| CR | Complete disappearance of all non-target disease; all nodes <10mm SAD; markers normalized (if used) |
| Non-CR / Non-PD | One or more non-target lesions persist but have not qualified as CR or progressed |
| Unequivocal Progression | Substantial worsening that clearly changes overall tumor burden |
| Not Evaluated | Non-target disease could not be assessed |
"SD" is NOT used for non-target lesions
The preferred terminology is “Non-CR/Non-PD” for persistent non-target disease. “Stable Disease” is reserved for target lesions. Using the correct terminology prevents confusion in clinical documentation and trial data.
Unequivocal Progression — The Key Concept
Unequivocal progression of non-target lesions triggers overall PD — even if all target lesions are in PR or CR. This is one of three independent PD triggers.
The bar for non-target PD is high:
Modest Increase Is Not Sufficient
A small or moderate increase in non-target disease does not qualify as unequivocal progression. The worsening must be substantial — enough to change overall tumor burden even in the setting of target lesion PR or SD.
Examples of Non-target PD
- Small/moderate pleural effusion at baseline → large/malignant effusion at follow-up
- Localized lymphangitic carcinomatosis → diffuse lymphangitic spread
- Leptomeningeal enhancement appearing where none was present
- Ascites that was absent or trace → new or worsening
- Bone lesion with soft tissue component developing a new soft tissue mass
What Does NOT Qualify
- A 2mm increase in a 12mm non-measurable liver lesion
- Minimal increase in size of small volume non-target disease
- Change in appearance related to treatment effect (necrosis, edema) without clear tumor progression
Non-target PD Overrides Target Response
Target lesions in PR (30%+ shrinkage) can coexist with unequivocal non-target progression, and the overall response is PD. Always assess non-targets independently — do not let target lesion response bias your non-target assessment.
Special Case: Non-target Only Patients
Patients may have no measurable disease at baseline — only non-target disease. In this case:
- There are no target lesions, no sum of diameters
- Overall response is based solely on non-target status and new lesions
- The response table for non-target-only patients differs:
| Non-Target | New Lesions | Overall |
|---|---|---|
| CR | No | CR |
| Non-CR/non-PD | No | Non-CR/non-PD |
| Unequivocal progression | Any | PD |
| Any | Yes | PD |
Note: “SD” is not used for this population — “Non-CR/non-PD” is the appropriate response category.
Nodes in Non-target Assessment
All lymph nodes — whether target or non-target — must have short axis <10mm for CR. Nodes ≥10mm SAD are pathological and:
- If ≥15mm SAD and selected → tracked as target (by SAD)
- If 10–14mm SAD or not selected → non-target (qualitative: present, absent, unequivocal progression)
Relationship to Overall Response
Non-target lesion status feeds into the master overall response table (see RECIST 1.1 Overview). Non-target CR, non-CR/non-PD, or unequivocal progression each determine overall response in combination with target and new lesion status.
Common Pitfall: Reader Bias
Research (ASCO 2025) shows that only ~15% of PD timepoints are driven by non-target progression alone. This suggests non-target PD is systematically under-detected — radiologists anchor on target lesion data and under-assess non-target disease. Treat non-target assessment as an independent, mandatory step.