The solitary use of the size of the tumor during evaluation for response to chemotherapy has some pitfalls and limitations, especially for specific tumors such as gastrointestinal stromal tumor (GIST).
The Choi response criteria for GIST proposed that tumor attenuation could provide an additional measure of response to imatinib therapy.
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Choi response criteria
Complete response
disappearance of all target lesions
no new lesions
Partial response
≥10% decrease tumor size on CT
or ≥15% decrease in tumor attenuation on CT
no progression of non-target lesions
no new lesions
Progressive disease
≥10% increase in sum of longest diameters of lesions
does not meet the criteria for partial response by virtue of tumor attenuation
new or growing intratumoral nodules
new lesions
Stable disease
none of the above
no symptomatic deterioration that can be associated with tumor progression
Practical points
tumor size is represented by the sum of the longest cross-sectional diameters for target lesions similarly to RECIST
tumor attenuation was measured in the portal venous phase in the original study 2
Modified Choi (mChoi) system
First proposed for metastatic renal cell cancer treated with tyrosine kinase inhibitors, the mChoi system has one major difference: both 10% decrease in size and 15% CT density are required for the diagnosis of partial response. In this setting the mChoi system was found to correlate better with time to disease progression 3.
See also
online calculator: https://radcalculators.org/choi-response-criteria-calculator/
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