RECIST 1.1: comparison with RECIST 1.0

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

Fundamental concept common to both versions of RECIST: measurable lesions are those you CAN measure (determined at baseline). From these, select the target lesions as the ones you actually DO measure. 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)
• Upup to 10 target lesions total, up to 5 per organ
• measurement: longest dimension (LD)
• PD (progressive disease): 20% increased in LD from Nadir
• non-measurable assessment: unequivocal progression
• lymph node measurements: none
• PET: not available
• Confirmationconfirmation of PR or CR as best response is required

RECIST 1.1

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

Discussion

Looking back at RECIST 1.0, several changes in RECIST 1.1 stand out. The most important modifications are that the total number of target lesions has been halved, cystic tumours and osteolytic metastases with soft tissue components are now measureable (provided the soft-tissue component is measureable), short axis measurements are taken in case of lymph nodes, PD 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 ². Other features worth separate mention are:

Regarding imaging modalities, now a frontal chestradiograph may be used just like CT to measure and compare disease burden, though this is clearly not the preferred modality.

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

Fate of target lesions which become too small to measure confidently, but yet visible on follow-up: they should be assigned a default value of 5mm ²

Malignant mesothelioma is a circumferential tumour and not easily given to measurement of long axis diameter. A proposed method to consistently measure these lesions is to take maximum tumour depth at anatomically reproducible landmarks ² :

• CR 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 PD according to RECIST 1.1. for details please refer to reference ²
• 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.
• Ultrasound: remains unqualified for the purposes of RECIST

See also

• RECIST