Recent developments in anti-cancer therapies had created the need to think of new response evaluation techniques,
as past criteria did not explain nor completely correlate with all clinical tumor responses.
In 2009 Immuno-related response criteria (irRC) were created.
They address new patterns of response derived from the use of immunotherapeutic agents,
as they can induce a radiological pseudo-progression due to their power to stimulate the immune system («tumor inflammation»,
also called “flare-effect”) if we are to evaluate their response-stability-progression by main «classic» criteria (RECIST 1.1).
Fig. 1: Drawing: Mechanism of immunotherapy and "flare effect"
In some cases this growth or new lesions will be caused by this "flare-effect",
especially if this increase occurs within the compound-specific tumor flare window (normally in the first year of treatment),
so patients will need careful clinical assesment and a follow-up CT in no less than 4-6 weeks to either confirm or rule out progression.
|
RECIST 1.1
|
irRC
|
Measurable
lesions
|
≥15mm SA nodal lesions
≥10mm LA rest of lesions
|
≥ 5x5mm SAxLA (bidimensional)
|
Number of lesions
|
5 in total
Up to 2 in each organ
|
10 visceral + 5 cutaneous
Up to 5 in each organ
|
Response criteria related to size
|
PR: SOL decreases ≥30% (from baseline)
CR: all lesions disappear
all nodes with SA ≤ 5mm
PD: SOL increases
≥20% (from nadir)
|
PR: sum (of products) of lesions decrease ≥50% (from baseline)
CR: all lesions disappear
all nodes with SA ≤ 5mm
PD: sum (of products) of lesions increases
≥25% (from nadir)
Confirmation CT needed
|
SD: Above criteria not met
|
New lesions appear
|
Equals progression of disease
|
If measurable their size is added to the sum
|
Abbreviations: SA = short axis; LA = long axis; SOL = sum of lesions; PD = progression of disease; PR = partial response; CR = complete response; SD: stable disease;
It is also been studied and observed the much more simplicity,
accuracy and reproducibility of unidimensional measuring (just LA of target lesions) and a limited number of lesions,
so a mixture of RECIST 1.1 it’s what is being promoted now (although more studies with larger cohorts are needed).
Also,
sometimes a lesion getting hypoattenuated could also mean early response changes,
even when the size criteria are not met (like MASS criteria).
In the cases of classic CR and PR with immunotherapeutic agents a ≥4-weeks-confirmation is thought to perhaps not be needed,
as thresholds for irPR and irPD assessment are aligned with RECIST 1.1.
We therefore (at our hospital) started applying the irRC simulating RECIST 1.1.
In every exploration we cover cervical-thoracic-abdominal-pelvic territories with CT scan (with iv contrast injection,
being the abdominal territory in both arterial and portal phases and the pelvis territory at least in portal phase; 5 mm for axial slice thickness),
and more (brain CT/MRI,
limbs CT) if a previous relevant lesion was clinically suspected and confirmed by imaging.
|
irRC |
irRECIST(1.1)
|
Measurable lesions
|
≥ 5x5mm SAxLA
(bidimensional)
|
≥15mm SA nodal lesions
≥10mm LA rest of lesions
|
Number of lesions
|
10 visceral + 5 cutaneous
Up to 5 in each organ
|
5 in total
Up to 2 in each organ
|
Response criteria related to size
|
PR: sum (of products) of lesions decrease ≥50% (from baseline)
CR: all lesions disappear
all nodes with SA ≤ 5mm
PD: sum (of products) of lesions increases
≥25% (from nadir)
Confirmation needed for PR,
CR,
PD
|
PR: SOL decreases ≥30% (from baseline)
CR: all lesions disappear
all nodes with SA ≤ 5mm
PD: SOL increases
≥20% (from nadir)
Confirmation needed for PD
|
SD: Above criteria not met
|
New lesions appear
|
If measurable their size is added to the sum
|
Most other rules (neglected to some extent in irRC) regarding bone,
brain,
cystic-necrotic,
non-measurable and previously treated lesions,
may be taken into account following RECIST1.1.