The potential usefulness of the Response Index in positron emission tomography assessing the therapeutic effect of pre-operative chemotherapy for advanced colorectal cancer

Abstract

Background and purpose

Pre-operative chemotherapy is an option for patients with local advanced rectal cancer, but the response rate to pre-operative chemotherapy with oxaliplatin is still low. If the therapeutic effect of pre-operative chemotherapy could be assessed, we may be able to convert to surgery early. The purpose of the present study was to validate the correlation between the maximum standardized uptake value (SUV_max) in 18F-fluorodeoxyglucose positron emission tomography–computed tomography (PET–CT) of the primary tumor and the therapeutic effect of pre-operative chemotherapy in advanced colorectal cancer.

Patients and methods

Retrospective cohort study from January 2011 to October 2015. We examined 28 patients with pathologically confirmed sigmoid or rectal cancer that underwent pre-operative chemotherapy and surgery. The correlation between Response Index (RI), calculated as (SUV_max after chemotherapy)/(SUV_max before chemotherapy), and the therapeutic effect on the primary tumor in advanced colorectal cancer.

Results

The degree of differentiation (p = 0.04), SUV_max in the primary tumor after chemotherapy (p = 0.02), and RI (p = 0.008) were significant predictors of the therapeutic effect in univariate analysis. The areas under the ROC curve constructed with RI and therapeutic effect was 0.77. The optimal cut-off values for the RI in the responder group was < 0.32.

Conclusion

RI calculated as (SUV_max after chemotherapy)/(SUV_max before chemotherapy) in the primary tumor significantly correlated with the therapeutic effect of chemotherapy on advanced colorectal cancer. Thus, RI is potentially useful for predicting the therapeutic effect in advanced colorectal cancer.

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