Introduction

Efficacy assessment of solid tumour cancer is usually based on imaging (E.g. CT-Scan, MRI). In the past several attempts to define a standard criteria for solid tumor efficacy assessment were made:

  • 1979: WHO Tumour Response Criteria
  • 1992: SWOG revision of WHO criteria
  • 2000: Response Evaluation Criteria in Solid Tumours (RECIST 1.0)
  • 2008: Response Evaluation Criteria in Solid Tumours (RECIST 1.1)

These guidelines are standardizing solid tumour measurements and objective assessment definition for change in tumour size.

Recist

Today RECIST 1.1 despite some existing criticism, is the recognized standard approach for defining tumor response for solid tumors and therefore for defining the Progression Free Survival (PFS). RECIST is a validated and « simplified » version of WHO specifically to be used in adult and paediatric cancer clinical trials (not in malignant brain tumour or malignant lymphoma studies).

MEASURABLE LESION or TARGET LESION It can be measured in one diameter:

  • Longest Diameter (LD) 20 mm at least with conventional techniques
  • Longest Diameter (LD) 10 mm with spiral CT scan

RECIST recommends a maximum of 10 measurable lesions (biggest and most suitable for repeated measures), maximum 5 measurable lesions per organ.

NON MEASURABLE LESION or NON TARGET LESION All other lesions, for example:

  • LD < 20 mm with conventional techniques
  • LD < 10 mm with spiral CT scan
  • Truly non-measurable lesions (e.g bone)

Often having at least one measurable lesion is an eligibility criteria to enter into the study. RECIST recommends to perform a tumor assessment at regular intervals (usually every 2 cycles).

An assessment time-point is considered valid for the overall response evaluation if:

  • All baseline lesions are assessed at the time point
  • All lesions are assessed with the method used at baseline

Definition of Best Overall Tumor Response

The Best Overall Response (BOR) is the best response recorded from the start of the study treatment until the disease progression/recurrence:

  • Complete Response (CR) upon confirmation at least 4 wks of 1st CR
  • Partial Response (PR) upon confirmation at least 4 wks of first PR
  • Stable Disease (SD)
  • Progressive Disease (PD)

A requirement for SD is that it should be met at least once no less than 6-8 weeks after the first dose of trial treatment/baseline assessment, otherwise the best response will be Not Evaluable (NE). The criteria for confirmation of the response is summarized in the following table:

Overall Response First Time PointOverall Response Subsequent Time PointBest Overall Response
RCRCR
CRPRSD,PD or PR (a)
CRSDSD (b)
CRPDSD (b)
CRNESD (b)
PRCRPR
PRPRPR
PRSDSD
PRPDSD (b)
PRNESD (b)
NENENE

Definition of Time Point Overall Response

Target Lesions Response:

  • Complete Response (CR) Disappearance of all target lesions (sum of all target lesions=0)
  • Partial Response (PR) >=30% decrease (vs baseline) of sum of all target lesions dimension
  • Progressive Disease (PD) new lesions or >=20% increase (vs smallest sum of target lesions or nadir)
  • Stable Disease (SD) when sum of all target lesions does not qualify for CR/PR/PD

Non Target Lesions Response:

  • Complete Response (CR) Disappearance of all non-target lesions
  • Stable Disease (SD) Persistence of non-target lesions
  • Progressive Disease (PD) New lesions

The time-point overall response is then derived according to the criteria reported in the following table:

Target Lesions Non Target LesionsNew LesionsOverall Response
CRCRNoCR
CRNon CR/Non PDNoPR
CRNot evaluatedNoPR
PRNon-PD/Not all evaluatedNoPR
SDNon-PD/Not all evaluatedNoSD
Not all evaluatedNon-PDNoNE
PDAnyYes or NoPD
AnyPDYes or NoPD
AnyAnyYesPD

The objective response rate (the proportion of patients in whom a CR or PR was observed) could be also reported and analysed.

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