Preoperative assessment of malignant potential of gastrointestinal stromal tumor by dual-time-point 18F-fluorodeoxyglucose positron emission tomography imaging: Usefulness of standardized uptake value and retention index

Background: To evaluate the usefulness of preoperative imaging with F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) for noninvasive risk assessment of gastrointestinal stromal tumor (GIST). Materials and Methods: A retrospective review including 32 patients with pathologically proven GIST. Preoperative FDG-PET scan results including maximum standardized uptake values (SUVs) of the GISTs at 1 h postinjection (SUV1) were available for all tumors and SUVs at 2 h postinjection (SUV2) were available for 22 tumors. When both SUV1 and SUV2 were available, a retention index (RI, %) was calculated, and the correlation of these PET parameters with the histopathologic results was analyzed. Results: SUV1 was significantly higher in tumors in the high-risk group (6.0 ± 2.7) compared to those in the low risk (3.0 ± 1.6) or very low-risk (2.7 ± 1.2) groups (P = 0.009 and 0.011, respectively). At a cutoff of 5.2, the SUV1 demonstrated sensitivity of 80% and a specificity of 89% for predicting high-risk GISTs. Tumor size was significantly correlated with SUV1 (r = 0.68, P < 0.001) and SUV2 (r = 0.66, P = 0.001), and SUV1, SUV2, and RI were significantly higher in tumors with mitotic index > 5/50 high-power field than in those with lower mitotic index. RI was significantly higher in tumors with C-kit mutation than in those with no C-kit mutation. Conclusion: SUV1 measured during preoperative FDG-PET imaging correlated well with malignant potential of GISTs, especially for high-risk versus Low-/very-low-risk tumors. RI values correlated well with mitotic counts and C-kit mutation, suggesting that this mutation may have some influence on tumor metabolism.