Clinical significance of performing 18F-FDG PET on patients with gastrointestinal stromal tumors: a summary of a Japanese multicenter study

English version of Japanese Clinical Practice Guidelines 2022 for gastrointestinal stromal tumor (GIST) issued by the Japan Society of Clinical Oncology

The Japan Society of Clinical Oncology Clinical Practice Guidelines 2022 for gastrointestinal stromal tumor (GIST) have been published in accordance with the Minds Manual for Guideline Development 2014 and 2017. A specialized team independent of the working group for the revision performed a systematic review. Since GIST is a rare type of tumor, clinical evidence is not sufficient to answer several clinical and background questions. Thus, in these guidelines, we considered that consensus among the experts who manage GIST, the balance between benefits and harms, patients' wishes, medical economic perspective, etc. are important considerations in addition to the evidence. Although guidelines for the treatment of GIST have also been published by the National Comprehensive Cancer Network (NCCN) and the European Society for Medical Oncology (ESMO), there are some differences between the treatments proposed in those guidelines and the treatments in the present guidelines because of the differences in health insurance systems among countries.

Metabolic behavior and prognostic role of pretreatment 18F-FDG PET/CT in gist

AIM

The metabolic behavior and the prognostic value of ¹⁸ F-FDG-PET/CT in gastrointestinal stromal tumor (GIST) is not well investigated. The aim of this study was to analyze the metabolic behavior of GIST and the prognostic role of pretreatment PET/CT features.

METHODS

In this retrospective study, we included 35 patients with a diagnosis of GIST who underwent a pretreatment ¹⁸ F-FDG-PET/CT scan. We analyzed PET images visually and semiquantitatively by measuring several metabolic parameters as the maximum standardized uptake value corrected for body weight (SUVbw), for lean body mass (SUVlbm), for body surface area (SUVbsa), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). The Kaplan-Meier method was used to measure the progression free survival (PFS) and overall survival curves.

RESULTS

Twenty-nine (82%) patients showed a positive ¹⁸ F-FDG-PET/CT, whereas the remaining 6 had no hypermetabolic lesions. ¹⁸ F-FDG-avidity was significantly related with mitotic index, tumor stage and tumor risk group. Instead, semiquantitative PET/CT parameters correlated only with tumor risk group. Disease progression occurred in 16 patients whereas death in seven. ¹⁸ F-FDG-avidity, MTV and TLG were the only variables significantly associated with PFS.

CONCLUSION

An 82% rate of PET avidity in GIST was found and it was correlated with stage, tumor risk group and mitotic index. Only baseline ¹⁸ F-FDG-avidity, MTV and TLG were independently correlated with PFS.

Diagnostic Role of 18F-Fluorodeoxyglucose Positron Emission Tomography in Gastric Mesenchymal Tumors

There have been no comparative studies investigating the results of 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) in patients with gastric mesenchymal tumors, including leiomyomas, leiomyosarcomas, schwannomas, and gastrointestinal stromal tumors (GISTs). We retrospectively reviewed the data of 142 patients with pathologically diagnosed gastric mesenchymal tumors treated at 11 institutions. We analyzed the correlation between the maximum standardized uptake value (SUVmax) evaluated using fluorodeoxyglucose-positron emission tomography (FDG-PET) and the tumor size. The correlation between the SUVmax and mitotic index was also investigated in GISTs. The SUVmax (mean ± standard deviation) was 0.5 ± 0.6 in very low-risk GISTs (n = 42), 2.1 ± 0.7 in low-risk GISTs (n = 26), 4.9 ± 0.8 in intermediate-risk GISTs (n = 22), 12.3 ± 0.8 in high-risk GISTs (n = 20), 1.0 ± 1.0 in leiomyomas (n = 15), 6.9 ± 1.2 in schwannomas (n = 10), and 3.5 in a leiomyosarcoma (n = 1). The SUVmax of GISTs with an undetermined risk classification was 4.2 ± 1.3 (n = 8). Linear associations were observed between the SUVmax and tumor size in GISTs, leiomyomas, and schwannomas. The SUVmax of GISTs with a high mitotic index was significantly higher than that of GISTs with a low mitotic index (9.6 ± 7.6 vs. 2.4 ± 4.2). In conclusion, we observed positive correlations between the SUVmax and tumor size in GISTs, leiomyomas, and schwannomas. The SUVmax also positively correlated with the mitotic index and risk grade in GISTs. Schwannomas showed a higher FDG uptake than GISTs and leiomyomas.

Role of 18F-FDG PET/CT in restaging and follow-up of patients with GIST

PURPOSE

Gastrointestinal stromal tumor (GIST) is a rare tumor with high risk of recurrence and poor prognosis in case of advanced GIST. The aim of this study was to evaluate the possible role of 18F-FDG PET/CT in restaging GIST.

METHODS

Fifty-four patients (30 male) with histological proven GIST underwent 100 18F-FDG PET/CT for restaging in suspected recurrence or during follow-up. Histopathology results and/or clinical/imaging follow-up for at least 12 months were considered as reference standard. Moreover, the diagnostic accuracy and clinical impact of 18F-FDG PET/CT were calculated.

RESULTS

Twenty-seven (27%) 18F-FDG PET/CT were positive, while the remaining 73 (73%) were negative. Sensitivity, specificity, PPV, NPV, and accuracy of PET/CT were 89% (95% CI 72-98%), 97% (95% CI 90-100%), 93% (95% CI 76-98%), 96% (95% CI 89-98%), and 95% (95% CI 89-98%). 18F-FDG PET/CT had a positive clinical impact in 18/100 studies changing the management, in 8 cases switching from local therapy to systemic therapy due to the detection of disseminate disease at PET/CT, in three cases recognizing relapse not detected by conventional imaging, and in 7 cases demonstrating to be true negative and avoiding unnecessary therapies.

CONCLUSIONS

18F-FDG PET/CT seems to be an accurate method for detection and localization of local and distant recurrence in GIST with good sensitivity and specificity and significant impact on clinical decision-making.

Performance of F-18 FDG PET/CT for predicting malignant potential of gastrointestinal stromal tumors: A systematic review and meta-analysis

BACKGROUND AND AIM

We aimed to explore the role of the diagnostic accuracy of F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) or positron emission tomography/computed tomography (PET/CT) for prediction of malignant potential of gastrointestinal stromal tumor (GIST) through a systematic review and meta-analysis.

METHODS

The MEDLINE, Embase, and Cochrane Library database, from the earliest available date of indexing through May 31, 2017, were searched for studies evaluating the diagnostic performance of F-18 FDG PET or PET/CT for prediction of malignant potential of GIST. We determined the sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic curves.

RESULTS

Across seven studies (188 patients), the pooled sensitivity for F-18 FDG PET or PET/CT was 0.88 (95% confidence interval [CI]: 0.80-0.94) without heterogeneity (χ²  = 6.15, P = 0.72) and a pooled specificity of 0.88 (95% CI: 0.75-0.94) with heterogeneity (χ²  = 23.2, P = 0.01). LR syntheses gave an overall LR+ of 7.2 (95% CI: 3.3-15.3) and LR- of 0.13 (95% CI: 0.07-0.24). The pooled diagnostic odds ratio was 54 (95% CI: 16-181).

CONCLUSION

F-18 FDG PET or PET/CT demonstrated good sensitivity and specificity for the prediction of malignant potential of GIST. At present, the literature regarding the use of F-18 FDG PET or PET/CT for the prediction of malignant potential of GIST remains still limited; thus, further large multicenter studies would be necessary to substantiate the diagnostic accuracy of F-18 FDG PET or PET/CT prediction of malignant potential of GIST.

Value of FDG PET/CT in Patient Management and Outcome of Skeletal and Soft Tissue Sarcomas

Fluorodeoxyglucose (FDG)-PET/computed tomography (CT) has been increasingly used in bone and soft tissue sarcomas and provides advantages in the initial tumor staging, tumor grading, therapy assessment, and recurrence detection. FDG-PET/CT metabolic parameters are reliable predictors of survival in sarcomas and could be implemented in risk stratification models along with other prognostic factors in these patients.

Imaging features of primary anorectal gastrointestinal stromal tumors with clinical and pathologic correlation

Purpose: To evaluate the imaging features of anorectal gastrointestinal stromal tumors (GISTs) with clinical and histopathologic correlation. Materials and methods: In this Institutional Review Board-approved, Health Insurance Portability and Accountability Act-compliant retrospective study, 16 patients (12 men; mean age 66 years (30–89 years)) with pathologically proven anorectal GISTs seen at our institution from January 2001 to July 2011 were identified. Electronic medical records were reviewed to obtain clinical data. Pretreatment imaging studies (computed tomography (CT) in 16 patients, magnetic resonance imaging (MRI) in 9 patients and fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT in 8 patients) were evaluated by 2 radiologists until consensus. The location, size and imaging features of the primary tumor and metastases at presentation, if any, were recorded, and correlated with clinical data and pathologic features (histologic type, presence of necrosis, mitotic activity, risk category, immunohistochemical profile). Results: The mean tumor size was 6.9 × 6.0 cm. Of the 16 tumors, 11 (68.7%) were infralevator, 4 (25%) supra and infralevator and 1 (6.3%) supralevator; 9 (56.2%) were exophytic, 6 (37.5%) both exophytic and intraluminal, and 1 (6.3%) was intraluminal. The tumors were iso- to minimally hypoattenuating to muscle on CT, iso- to minimally hypointense on T1-weighted images, hyperintense on T2-weighted images and showed variable enhancement. Necrosis was seen in 4 (25%), and hemorrhage and calcification in 2 (12.5%) patients each. The tumors were FDG avid with a mean maximum standardized uptake value of 11 (8.4–16.8). All tumors were positive for KIT and CD34. Distant metastasis to liver was seen in 1 patient (6.3%) at presentation. Conclusion: Anorectal GISTs are well-circumscribed, non-circumferential, predominantly infralevator, intramural or exophytic, FDG-avid, hypoattenuating masses, and present without lymphadenopathy or intestinal obstruction.

Consensus report on the radiological management of patients with gastrointestinal stromal tumours (GIST): recommendations of the German GIST Imaging Working Group

The aim was to reach consensus in imaging for staging and follow-up as well as for therapy response assessment in patients with gastrointestinal stromal tumours (GIST). The German GIST Imaging Working Group was formed by 9 radiologists engaged in assessing patients with GIST treated with targeted therapy. The following topics were discussed: indication and optimal acquisition techniques of computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET)/CT; tumour response assessment considering response criteria and measurement techniques on CT, MRI and PET/CT; result interpretation; staging interval and pitfalls. Contrast-enhanced CT is the standard method for GIST imaging. MRI is the method of choice in case of liver-specific questions or contraindications to CT. PET/CT should be used for early response assessment or inconclusive results on morphologic imaging. All imaging techniques should be standardized allowing a reliable response assessment. Response has to be assessed with respect to lesion size, lesion density and appearance of new lesions. A critical issue is pseudoprogression due to myxoid degeneration or intratumoural haemorrhage. The management of patients with GIST receiving a targeted therapy requires a standardized algorithm for imaging and an appropriate response assessment with respect to changes in lesion size and density.

Glucose transporter expression of an esophageal gastrointestinal tumor detected by F-18 FDG PET/CT

A 74-year-old woman had dysphagia and underwent esophagogastroduodenoscopy. A giant submucosal tumor was seen from the middle to the lower esophagus. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG-PET/CT) was performed and F-18 FDG was found to accumulate in the submucosal tumor. The maximum standardized uptake value of the early phase was 4.93 and that of the delayed phase was 6.48. Gastrointestinal stromal tumor (GIST) was confirmed by both fine needle aspiration under endoscopic ultrasound and postoperative histopathologic findings. We stained the postoperative histopathologic specimen to investigate glucose transporter (GLUT) expression using immunohistochemistry, which revealed that GLUT-1 had a weak expression on membranes and GLUT-4 had a strong expression on membranes or in cytoplasm. GLUT-3 had no expression on membranes or in cytoplasm. Esophageal GIST is rare and the relationship between GLUT expression and F-18 FDG accumulation in GIST is probably rare.

[Molecular imaging of the small intestine]

Molecular imaging uses the molecular signature of cells for targeted minimally-invasive detection and characterization of gastrointestinal pathologies. Exogenous fluorescent agents serve as molecular beacons for visualization of specific surface markers or metabolic activity in the target tissue. Molecular imaging with radioactively labeled substances is well established in nuclear medicine for wide-field detection of lesions in the small intestine. In gastrointestinal endoscopy, both macroscopic detection by endogenous or exogenous fluorescence and microscopic visualization by endomicroscopy have been investigated in clinical trials, however have not yet been evaluated in larger patient cohorts. Still, molecular imaging has the potential to greatly enhance our understanding of gastrointestinal pathology and to impact on future clinical algorithms and science in gastroenterology.