The Usefulness of Preoperative 18FDG Positron-Emission Tomography and Computed Tomography for Predicting the Malignant Potential of Gastrointestinal Stromal Tumors

Background: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The tumor size and mitotic count, typical risk category factors, are difficult to determine preoperatively. This study aimed to evaluate the usefulness of preoperative 18F-fluoro-2-deoxyglucose positron-emission tomography/computed tomography (18FDG-PET/CT) for predicting the malignant potential of GISTs by analyzing the correlation between the maximum standardized uptake value (SUVmax) and postoperative factors. Methods: Thirty consecutive patients underwent surgery after preoperative 18FDG-PET/CT and were diagnosed with pathologically confirmed GIST. The tumor size, mitotic count, MIB-1 index and National Institutes of Health (NIH) risk category were compared with SUVmax. Results: Significant correlations between SUVmax and tumor size and NIH risk category were determined. The sensitivity and specificity of SUVmax for predicting the risk of malignancy were 85.7 and 62.5%, respectively. The optimal cut-off value for SUVmax was 3.0 between patients classified into low-risk and high-risk malignancy groups. There was no significant correlation between SUVmax and mitotic count or MIB-1 index. Multivariate analysis indicated that SUVmax was the only predictive risk factor in the high-risk malignancy group. Conclusions: 18FDG-PET/CT is useful for assessing the malignant potential and bioactivity of GISTs. When SUVmax is >3.0, the tumor must be resected even if it measures <2 cm, because of its high malignant potential.