Choi response criteria

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. 

Complete response

• Disappearance of all target lesions  
• no new lesions 

Partial response

• ≥10% decrease tumor size at computed tomography (CT)
• or ≥15% decrease in tumor attenuation at computed tomography (CT)
• no progression of non-target lesions
• no new lesions 

Progressive disease

• ≥10% increase in sum of longest diameters (SLD) 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. 

Online calculators

https://radcalculators.org/choi-response-criteria-calculator/

See also

• RECIST