RECIST 1.1: comparison with RECIST 1.0

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Response Evaluation Criteria In Solid Tumors (RECIST) was updated to version 1.1 in 2009.

For both RECIST 1.0 and 1.1, the requirement for measurable disease at baseline depends on the endpoints of the clinical trial.

The fundamental concept common to both versions of RECIST is that measurable lesions are those that can be measured (determined at baseline). From these, the target lesions selected are the ones that are actually measured. From that point forward: once target, always target (and once non-target, always non-target).

The differences between RECIST 1.1 and RECIST 1.0 are as follows:

RECIST 1.0

  • minimum measurable lesion size
    • ≥10 mm (spiral CT)
    • ≥20 mm (conventional CT, MRI)
  • up to 10 target lesions total, up to 5 per organ
  • measurement: longest dimension (LD)
  • PD (progressive disease): 20% increase in LD from nadir
  • non-measurable assessment: unequivocal progression
  • lymph node measurements: none
  • PET: not available
  • confirmation of partial response (PR) or complete response (CR) as best response is required

RECIST 1.1

  • measurement: longest dimension, but for lymph nodes short axis dimension
  • minimum measurable lesion size
    • long axis ≥10 mm (CT/MRI) and 2 x slice thickness, if the slice thickness is >5 mm
    • long axis ≥20 mm on chest x-ray
    • lymph nodes: short axis ≥15 mm
  • up to 5 target lesions total, up to 2 per organ
  • PD: same as 1.0, but the increase should also be >5 mm from nadir
  • non-measurable assessment: substantial worsening/tumor burden has increased sufficiently
  • lymph node measurements (specific instructions):
    • short axis ≥15 mm is measurable
    • 10-14 mm is abnormal (recorded as non-target)
    • <10 mm is considered normal
  • PET: may be considered to support CT, primarily for PD (detection of new lesions) or confirmation of CR
  • confirmation of partial (PR) or complete response (CR) is required only for non-randomized trials in which the ORR (objective response rate) is a key endpoint

Discussion

Looking back at RECIST 1.0, several changes in RECIST 1.1 stand out.

Lesion selection

The most important modifications are that the total number of target lesions has been halved, (from 10 to 5). Cystic tumors and osteolytic metastases with soft tissue components can now be included (provided the soft-tissue component is measurable).

Measurement

Lymph node measurement is explicitly performed along the short axis. Progressive disease (PD) is based on non-target lesions is clearly defined, and a minimum 5 mm absolute increase is needed in addition to a 20% increase for PD.

Target lesions which fragment into several smaller ones or coalesce into a larger single one are still measured, except that in the former case the longest dimensions of individual entities are measured and may thus differ in orientation.

If target lesions remain visible on follow-up but are too small to confidently measure with accuracy, they should be assigned a measurement of 5 mm .

Modalities
  • frontal chest radiograph may be used - like CT - to measure and compare disease burden, though this is clearly not the preferred modality
  • PET is now included
    • usually to assess progression or confirm complete response
  • ultrasound remains unqualified for the purposes of RECIST
Applications in specific malignancies

Malignant mesothelioma is a circumferential tumor and so not easy to establish a long axis diameter. A proposed method to consistently measure these lesions is to take maximum tumor depth at anatomically reproducible landmarks :

  • complete response in lymph nodes: this is defined as nodal short axis diameter of <10 mm on follow-up (as opposed to disappearance in target lesions)
  • lesion in an area not covered at baseline: this is considered to be progressive disease (PD) according to RECIST 1.1
  • equivocal new lesions: a clear-cut new lesion, i.e. one not attributable to technical difference between examinations or pathology besides metastases, is evidence of PD. However, equivocal new lesions should be followed until their nature is certain. Once they are confirmed as new lesions, PD is assigned to the date where they were first seen.

See also