Measurable Disease
title: “Measurable Disease” type: descriptor category: recist/descriptor tags: [recist, measurable-disease, baseline, measurement] sources:
- file: “recist_eisenhauer_2009.pdf” page: “229-232” date_created: 2025-04-15 date_modified: 2025-04-15 confidence: high anki_deck: “Radiology::RECIST” weak_area: false
Definition
Measurable disease is tumor that can be accurately and reproducibly measured at baseline. Only patients with measurable disease should be included in trials where objective tumor response (ORR) is the primary endpoint. Patients with non-measurable disease only may still be eligible for trials using PFS or TTP as endpoints.
Measurable Lesion Criteria
Solid (Extra-nodal) Lesions
- Longest diameter ≥10mm on spiral CT
- CT slice thickness ≤5mm (contiguous or spiral cuts ≤5mm)
- Lesions measured in the plane of measurement — record the single longest diameter
Lymph Node (Nodal) Lesions
- Short axis diameter ≥15mm
- Short axis = the largest diameter perpendicular to the long axis of the node
- Short axis is used because it is the most reproducible measurement — least affected by imaging plane
Nodes vs. All Other Lesions
Every lesion type EXCEPT lymph nodes is measured by longest diameter. Lymph nodes are the only lesion type measured by short axis diameter.
Node Classification by Size
| Short Axis Diameter | Classification | Role in RECIST |
|---|---|---|
| <10mm | Normal | Not recorded; not measurable |
| 10–14mm | Pathological but non-measurable | Non-target only |
| ≥15mm | Pathological and measurable | Target or non-target eligible |
Nodes <10mm short axis are considered normal. Nodes 10–14mm are abnormal but too small for reliable measurement — they can only be followed as non-target lesions.
Non-Measurable Disease
Lesions Below Threshold
- Solid lesions with longest diameter <10mm
- Lymph nodes with short axis 10–14mm (pathological but non-measurable)
Truly Non-Measurable Disease
Cannot be measured by any reproducible method:
- Bone-only metastases (lytic or blastic without soft tissue component)
- Leptomeningeal carcinomatosis
- Ascites or pleural/pericardial effusions
- Inflammatory breast disease
- Lymphangitic carcinomatosis of lung or skin
- Cystic or necrotic lesions without a measurable solid component
- Lesions in irradiated fields (if the irradiated site is the only site of disease)
Cavitating Lesions
Cavitating lesions should not be selected as target lesions — the cavity can change size independent of tumor response. However, cystic or necrotic lesions can be selected as targets if the solid/enhancing portion is ≥10mm and can be reproducibly measured.
Imaging Modality Requirements
CT — Standard Method
- Spiral CT with ≤5mm contiguous slice thickness
- Current standard for target lesion measurement
- 10mm threshold established with this technique in mind
MRI
- Acceptable alternative to CT
- Must meet same measurability criteria
- Same slice thickness requirements apply
Chest X-ray
- Can measure lesions ≥20mm only
- Not useful for most modern trial work
- Historical modality
What CANNOT Be Used
- Ultrasound — not reproducible for serial measurement
- Conventional radiography — insufficient resolution
- Endoscopy — not standardized for serial measurement
- FDG-PET — not used for measuring existing target lesions (see New Lesions for its role)
Eligibility Implications
- Protocols where ORR is the primary endpoint require measurable disease at baseline
- Trials using PFS or OS as primary endpoints may enroll patients with non-measurable disease only
- All disease — measurable and non-measurable — must be documented at baseline
- Non-measurable disease is followed as non-target lesions (see Non-target Lesions)
Selection of Target Lesions from Measurable Disease
Not all measurable lesions become targets. Up to 5 target lesions (max 2 per organ) are selected. See Target Lesions.
Measurable lesions not selected as targets become non-target lesions — followed qualitatively but not measured.