RECIST 1.1 Target Lesion Selection
RECIST 1.1 Target Lesion Selection
Is this lesion measurable, and can it be a RECIST 1.1 target? The size threshold depends on what the lesion is, what it was imaged with and how thick the slices were — and a lymph node is measured on its short axis against entirely different numbers.
RECIST 1.1 measurability and target eligibility
Lesion, modality and size to eligibilityNon-nodal lesion, 12 mm longest diameter, CT with 5 mm slices, no special feature
Measurability under RECIST 1.1
10 mm on CT or MRI with slice thickness 5 mm or less · twice the slice thickness where thicker · 20 mm on a chest radiograph · 10 mm by calliper on clinical examination
Lymph node, SHORT axis on CT:
15 mm or more — measurable, eligible as a target lesion · 10 mm up to 15 mm — pathological, non-measurable, non-target · under 10 mm — non-pathological, not recorded
Target lesion limits — five in total, no more than two per organ
- the node trap
- one number, two answers. A 12 mm measurement is a measurable target lesion if it is a non-nodal lesion’s longest diameter, and a pathological non-measurable node if it is a node’s short axis. Nodes also enter the sum on their short axis, which is the only measurement in RECIST that is not a longest diameter
- the slice-thickness rule
- RECIST strongly recommends slices of 5 mm or less. Where they are thicker, the minimum measurable size becomes twice the slice thickness, so a 10 mm lesion on 8 mm slices is not measurable and a 16 mm one is. The rule only ever raises the minimum: thin slices do not take it below 10 mm
- bone
- blastic lesions are non-measurable. Lytic or mixed lytic-blastic lesions with an identifiable soft-tissue component can be measurable, and it is that soft-tissue component that gets measured, on CT or MRI. Bone scintigraphy, PET and plain films are not adequate for measurement, though they can confirm presence or disappearance
- cysts
- two different things that get confused. A lesion meeting the criteria for a radiographically simple cyst is not a malignant lesion and is not recorded as disease at all. A cystic metastasis is disease and can be measurable, but a solid lesion is the preferred target where one exists
Worked example
Non-nodal lesion, 12 mm longest diameter, CT with 5 mm slices, no special feature
No special feature, so the size rules apply
Non-nodal lesion on CT with slices of 5 mm or less → the minimum is 10 mm
12 mm is at or above 10 mm → measurable, eligible as a target lesion, subject to the limits of five targets in total and two per organ
Change the lesion type to a lymph node and the same 12 mm — now a short axis — becomes pathological but non-measurable, because a node needs 15 mm. One number, two answers
Keep CT but set the slice thickness to 8 mm: the minimum becomes twice that, 16 mm, so 12 mm is again non-measurable — and a 16 mm lesion on the same study would be measurable
Set the special feature to a blastic bone lesion and size stops mattering: non-measurable at any diameter
Minimum measurable size, by what the lesion is and how it was imaged
| Lesion | Modality | Minimum | If it falls short |
|---|---|---|---|
| Non-nodal | CT or MRI, slices 5 mm or less | 10 mm longest diameter | Non-target |
| Non-nodal | CT, slices over 5 mm | Twice the slice thickness | Non-target |
| Non-nodal | Chest radiograph | 20 mm longest diameter | Non-target |
| Non-nodal | Clinical examination, callipers | 10 mm, superficial lesion | Non-target |
| Lymph node | CT | 15 mm SHORT axis | Pathological non-target at 10 mm up to 15 mm; not recorded under 10 mm |
Lesions whose measurability does not depend on size
| Lesion | Status under RECIST 1.1 |
|---|---|
| Blastic bone lesion | Non-measurable. Record as non-target |
| Lytic or mixed bone lesion with an identifiable soft-tissue component | The soft-tissue component may be measurable on CT or MRI, and is what is measured |
| Radiographically simple cyst | Not considered a malignant lesion. Not recorded as disease |
| Cystic metastasis | May be measurable, but prefer a non-cystic lesion as target where one exists |
| In a previously irradiated or locally treated area | Usually not measurable unless progression in that lesion has been demonstrated since |
| Leptomeningeal disease, ascites, pleural or pericardial effusion, inflammatory breast disease, lymphangitic involvement | Truly non-measurable at any extent. Always non-target |
| Abdominal mass or organomegaly on examination, not confirmed by imaging | Non-measurable |
Selection happens once, and it decides everything after it
Target lesion selection is made at baseline and it is not revisited. Every subsequent response assessment is computed on the lesions chosen at the start, so a selection error does not announce itself at the next scan — it quietly biases every assessment the patient will ever have. That is why these rules are worth reading carefully once rather than approximating from memory.
The structure is simple enough. Up to five lesions in total, no more than two per organ, chosen from the lesions that are measurable. Paired organs such as the lungs or the kidneys count as one organ, and the nodal regions likewise count as one, so a patient with disease in several nodal chains contributes at most two nodal targets. The working group cut the limit from ten lesions to five on evidence rather than preference, stating that a data warehouse analysis showed no loss of information in doing so.
Measurability is where it gets specific, and the thresholds are not one number. A non-nodal lesion needs a longest diameter of 10 mm on CT or MRI with slices of 5 mm or less, 20 mm on a chest radiograph, or 10 mm by calliper if it is superficial enough to measure clinically. Where the slices are thicker than 5 mm — which RECIST discourages but does not forbid — the minimum becomes twice the slice thickness, so a 12 mm lesion on 8 mm slices is not measurable while the same lesion on 5 mm slices is. A lymph node is different in two ways at once: it is measured on its short axis, not its longest diameter, and its thresholds are its own. At 15 mm or more it is measurable and can be a target. Between 10 mm and 15 mm it is pathological but non-measurable, and goes down as non-target disease. Under 10 mm it is non-pathological and is not recorded as disease at all. The practical consequence is that one measurement — say 12 mm — means a measurable target lesion or a non-measurable node depending entirely on which structure it came from.
Finally there are the lesions whose status has nothing to do with their size. Blastic bone lesions are non-measurable, while a lytic or mixed lesion with an identifiable soft-tissue component is measured on that component. A radiographically simple cyst is not disease at all. A cystic metastasis is disease and can be measurable, but a solid lesion is the better target because a cyst’s dimensions move with its fluid as well as its tumour. A lesion in a previously irradiated field is usually not measurable unless progression there has been documented since. And leptomeningeal disease, ascites, effusions, inflammatory breast disease and lymphangitic spread are never measurable at any extent. None are inert: as non-target disease they can still deliver progression, which the RECIST 1.1 response category interpreter handles. A figure from a cohort is not this patient’s outcome and a response category is not a diagnosis: a stratum in which 42 per cent were alive at fifteen years tells you about that stratum, not which 42 per cent. This page computes a published quantity and states the criteria behind it. It renders no dose, no prescription and no treatment decision — that is the treating team’s. Every coefficient, conversion factor and threshold here is attributed to the source it was read in and, where it is a prognostic figure, to its derivation cohort; where the treating protocol differs, the protocol takes precedence.
Frequently asked questions
How many target lesions can RECIST 1.1 have?
Five in total, with no more than two per organ. Paired organs such as the lungs count as one organ, and all nodal regions together count as one, so at most two nodal targets. RECIST 1.0 allowed ten and five; the reduction was made on a data warehouse analysis showing no loss of information.
What is the minimum size for a measurable lesion?
For a non-nodal lesion: 10 mm longest diameter on CT or MRI with slices of 5 mm or less, 20 mm on a chest radiograph, or 10 mm by calliper on clinical examination. Where slices exceed 5 mm the minimum becomes twice the slice thickness. For a lymph node it is a short axis of 15 mm or more on CT.
Why are lymph nodes measured on the short axis?
Because the short axis discriminates pathological enlargement far better than the long axis, which varies with the node’s orientation to the scan plane. RECIST 1.1 made it explicit, with three bands: 15 mm or more is measurable, 10 mm up to 15 mm is pathological but non-measurable, and under 10 mm is non-pathological. The short axis is also what enters the sum of diameters.
Are bone lesions measurable under RECIST?
It depends on the lesion. Blastic bone lesions are non-measurable. Lytic or mixed lytic-blastic lesions with an identifiable soft-tissue component can be measurable, and it is the soft-tissue component that is measured, on CT or MRI. Bone scintigraphy, PET and plain films are not adequate for measurement, although they can confirm presence or disappearance.
Does a lesion that was too small at baseline become a target later?
No. Target lesions are selected at baseline and the selection is not revisited, so a lesion recorded as non-target stays non-target even if a later study images it better or it grows past the threshold. Its growth can still contribute to unequivocal non-target progression.
Related calculators
References
- Eisenhauer EA, Therasse P, Bogaerts J, et al. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer. 2009;45(2):228–47.
- RECIST Working Group / EORTC. RECIST 1.1. recist.eortc.org.
- Nishino M, Jagannathan JP, Ramaiya NH, Van den Abbeele AD. Revised RECIST guideline version 1.1: what oncologists want to know and what radiologists need to know. AJR Am J Roentgenol. 2010;195(2):281–9.
- RECIST 1.1: summary of key facts and concepts. Society for Clinical Research Sites teaching module.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/