Primary tumor 18F-FDG avidity affects the performance of 18F-FDG PET/CT for detecting gastric cancer recurrence

The usefulness of ¹⁸F-FDG PET in gastric cancer recurrence is limited by low sensitivity. Given that detectability by PET is dependent on the tumor's metabolic characteristics, we tested whether the performance of PET for gastric cancer recurrence is enhanced in patients with ¹⁸F-FDG-avid primary tumors. Methods: Three hundred sixtyeight patients with advanced gastric cancer underwent ¹⁸F-FDG PET/CT for initial staging and for recurrence surveillance after curative surgery. On initial PET/CT, primary tumors were ¹⁸F-FDG-avid if they displayed focal uptake with an SUV_max 4 or more. Follow-up ¹⁸F-FDG PET/CT was evaluated for recurrent disease. Results: On initial PET/CT, the primary tumor was ¹⁸F-FDG-avid in 236 of 368 (64.1%) and nonavid in 132 patients (35.9%). During follow-up for 18.9 ± 13.3 mo, 72 patients (19.6%) had recurrence. Of the 63 PET scans with recurrence, 42 (66.7%) and 21 (33.3%) were scans of patients with ¹⁸F-FDG-avid and nonavid primary tumors, respectively. PET sensitivity was higher in scans of patients with ¹⁸F-FDG-avid than nonavid tumors for all recurrences (81.0% vs. 52.4%; P = 0.018) and nonanastomosis site recurrences (82.1% vs. 47.4%; P = 0.006). The sensitivity for detecting peritoneal recurrence was also higher for the avid tumor group. PET specificity was similarly high (97.1% and 97.5%) for both groups. Adding cell type and Lauren classification to tumor ¹⁸F-FDG avidity further enhanced PET sensitivity. Conclusion: Surveillance ¹⁸F-FDG PET/CT after resection of gastric cancer has significantly higher sensitivity in patients with ¹⁸F-FDG-avid primary tumors and may have greater value in this group.