Gastrointestinal and Hepatobiliary · Tumour response assessment · 1.0

mRECIST for hepatocellular carcinoma

Modified RECIST for HCC measures only arterially enhancing (viable) tumour rather than overall lesion size, making it suitable for response assessment after locoregional and systemic therapy.

Purpose

To assess treatment response in hepatocellular carcinoma by measuring the diameter of arterially enhancing (viable) tumour on contrast-enhanced CT or MRI, because necrosis induced by locoregional or systemic therapy is not captured by conventional size-based RECIST.

Response category	Definition for target lesions (viable tumour)	Reporting implication
Complete response (CR)	Disappearance of any intratumoural arterial enhancement in all target lesions.	No measurable viable tumour; state that residual non-enhancing tissue may persist.
Partial response (PR)	At least a 30% decrease in the sum of diameters of viable (arterially enhancing) target lesions, referenced to the baseline sum of diameters.	Objective response; supports continuation of the current treatment strategy.
Progressive disease (PD)	At least a 20% increase in the sum of diameters of viable target lesions, referenced to the smallest sum of diameters recorded since treatment started.	Triggers reassessment of treatment strategy; report new lesions separately.
Stable disease (SD)	Neither sufficient shrinkage for partial response nor sufficient increase for progressive disease.	Continue surveillance at the protocol interval.

How to use it

Measure only the arterially enhancing component of a target lesion in the arterial phase; necrotic, non-enhancing tissue is excluded from the measurement even though the overall lesion may appear unchanged or larger.
Target lesions must be suitable for repeat measurement: well demarcated, arterially enhancing at baseline, and adequately assessed on contrast-enhanced CT or MRI with a proper arterial phase.
Non-target lesions, portal vein tumour thrombus, ascites and pleural effusion are assessed qualitatively and are not measured as target lesions; cytological or imaging confirmation is advised before calling new effusions progression.
Any unequivocal new lesion, including a new intrahepatic HCC meeting diagnostic imaging criteria, denotes progressive disease irrespective of the target-lesion measurements.
mRECIST was developed for HCC and depends on hypervascularity; it is not transferable to non-hypervascular tumours and correlates imperfectly with RECIST 1.1, which measures whole-lesion size.

Common mistake

Measuring the whole lesion diameter rather than only the arterially enhancing viable component — this misclassifies a well-devascularised post-TACE lesion as stable disease when it is in fact a complete or partial response.

Exam pearl

mRECIST thresholds mirror RECIST 1.1 (30% decrease for PR, 20% increase for PD) but are applied to the sum of viable enhancing diameters, not total lesion size.

Viva questions

What does mRECIST measure that RECIST 1.1 does not?: mRECIST measures the diameter of the arterially enhancing, viable component of a target lesion, whereas RECIST 1.1 measures the whole lesion diameter regardless of necrosis.
Define complete response by mRECIST.: Disappearance of any intratumoural arterial enhancement in all target lesions.
What are the thresholds for partial response and progressive disease?: Partial response is at least a 30% decrease in the sum of viable enhancing target-lesion diameters from baseline; progressive disease is at least a 20% increase from the smallest sum recorded since treatment started.
Which lesion is unsuitable as an mRECIST target lesion?: A lesion that is not arterially enhancing at baseline, is poorly demarcated, or cannot be measured reproducibly on contrast-enhanced CT or MRI.
How are portal vein tumour thrombus and new ascites handled?: Both are non-target findings assessed qualitatively rather than measured; a new effusion or ascites should be confirmed as malignant before being called progression.
Why can mRECIST and RECIST 1.1 disagree after TACE?: A lesion may be largely necrotic yet unchanged or larger in overall size, giving stable disease by RECIST 1.1 but a partial or complete response by mRECIST.