The Relationship of SUV Value in PET-CT with Tumor Differentiation and Tumor Markers in Gastric Cancer

68 Ga-FAPI PET/CT Detection of Non-FDG-Avid Poorly Differentiated Adenocarcinoma of the Trachea

ABSTRACT

Primary tracheal adenocarcinoma is relatively rare in clinical practice. We describe the 68 Ga-FAPI-04 and 18 F-FDG PET/CT findings of primary poorly differentiated tracheal adenocarcinoma in a 48-year-old woman. In the present case, the tumor showed increased 68 Ga-FAPI uptake but not significant 18 F-FDG activity.

Preoperative prediction of the pathological stage of advanced gastric cancer by 18F-fluoro-2-deoxyglucose positron emission tomography

In recent years, the usefulness of neoadjuvant chemotherapy for resectable advanced gastric cancer, particularly stage III, has been reported. Preoperative staging is mainly determined by computed tomography (CT), and the usefulness of ¹⁸F-fluoro-2-deoxyglucose positron emission tomography/CT (FDG-PET/CT) for gastric cancer has been limited in usefulness. The study aimed to evaluate the usefulness of FDG-PET/CT in preoperative diagnosis of advanced gastric cancer. We retrospectively enrolled 113 patients with gastric cancer who underwent preoperative FDG-PET/CT. All patients underwent gastrectomy with lymph-node dissection. The maximum standardized uptake value (SUVmax) of the primary tumor (T-SUVmax) and lymph nodes (N-SUVmax) were measured for all patients. The cutoff values of T-SUVmax for pathological T3/4 from receiver operating characteristic analysis were 8.28 for differentiated and 4.32 for undifferentiated types. The T-SUVmax and N-SUVmax cutoff values for pathological lymph-node metastasis were 4.32 and 1.82, respectively. Multivariate analysis showed that T-SUVmax for differentiated types was a significant predictor of pathological T3/4, and N-SUVmax was a significant predictor of lymph-node metastasis. In conclusion, the SUVmax of FDG-PET/CT was a useful predictor of pathological T3/4 and lymph-node metastasis in gastric cancer. The diagnosis by preoperative FDG-PET/CT is promising to contribute a more accurate staging of gastric cancer than by CT scan alone.

Dual time point [18F]Flurodeoxyglucose (FDG) Positron Emission Tomography (PET)/Computed Tomography (CT) with water gastric distension in differentiation between malignant and benign gastric lesions

Objectives

To assess diagnostic accuracy and added value of dual time point ¹⁸F-FDG PET/CT after gastric distention using oral water in differentiating malignant from benign gastric lesions.

Methods

Patients (n = 30, 19 males, mean age 58.6 ± 16.4 years). All patients are known or suspected oncology patients. All patients underwent whole body ¹⁸F-FDG PET/CT scan and 2 h delayed PET/CT abdominal images following oral water gastric distension. The best cut off values for early SUVmax (SUVmax1), delayed SUVmax (SUVmax2) and SUVmax2-SUVmax1 (ΔSUVmax) to differentiate benign from malignant lesions were set based on ROC analysis. Data analyzed included in addition; age, sex and ¹⁸F-FDG uptake pattern in delayed images. Suspicious gastric lesions were correlated with biopsy in 18 patients (60 %) and with clinical and follow-up imaging (¹⁸F-FDG PET/CT, CT or MRI) in 12 patients (40 %). Unpaired t-test was used to compare the mean deference in continuous variables between patients with gastric malignancy and those with benign gastric lesions. Fisher's exact test was used to analyze categorical variables. Logistic regression analysis was performed to identify the most powerful factors to predict malignant lesions.

Results

Fifteen patients (50 %) had confirmed malignant gastric lesions. Patients with confirmed gastric malignancy were older (65 ± 13 vs 52 ± 17; p = 0.023) and had significantly higher mean ΔSUVmax (1.29 ± 1.76 vs -0.89 ± 1.59; p = 0.003). The mean SUVmax1 (6.99 ± 6.66 vs 5.31 ± 2.53; p = 0.367) and SUVmax2 (8.29 ± 7.41 vs 4.44 ± 3.34; p = 0.077) although both higher in patients with malignant lesions, they did not reach statistical significance. Sensitivity, specificity, PPV, NPV, and accuracy to detect malignant gastric lesions were highest for lesions with localized uptake pattern in delayed images post water oral contrast as well as for lesions with ΔSUVmax>0. Regression analysis revealed both variables as independent predictors for malignant lesions with odd ratios of 22.9 and 9.5 respectively and final model Chi-Square of 19.9 (p < 0.0001). The model correctly identified 12/15 (80 %) malignant lesions and 13/15 (86.7 %) benign lesions with 2 false positives confirmed as chronic active gastritis with helicobacter pylori and 3 false negatives including 1 signet ring gastric cancer and 1 low grade gastrointestinal stromal tumor (GIST), both with poor 18 F-FDG uptake.

Conclusion

Localized uptake pattern in delayed PET/CT images following gastric distention with oral water contrast as well as ΔSUVmax>0 are powerful independent variables to identify malignant gastric lesions with fairly high sensitivity and reasonable accuracy. Malignancies with inherently low ¹⁸F-FDG avidity are the main cause of false negatives while active gastritis is the main cause of false positives.