The relationship between HER2 expression and ¹⁸F-FDG in gastric carcinoma

The aim of this retrospective study was to evaluate the relationship between human epidermal growth factor receptor 2 (HER2) expression and fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) uptake in positron emission tomography with computed tomography (PET/CT) in gastric carcinoma.

Gastric carcinoma patients who had ¹⁸F-FDG PET/CT scans before treatment were enrolled in this study. Ninety PET/CT images were evaluated before resection or neoadjuvant treatment of 69 patients with gastric carcinoma who had HER2 examination tests. The maximum standardized uptake value (SUVmax) at early (SUV1) and delayed images (SUV2) if any were calculated. In addition, liver SUVmax was measured from the normal liver parenchyma at the dual time (SUV1 liver and SUV2 liver). Tumor-to-liver SUVmax ratio (TLR), retention indexes (RI) from SUVmax, and TLR values obtained from dual-time images were calculated.

Histological type of 69 patients were 85.5% adenocarcinoma, 10.1% signet ring cell carcinoma, 2.9% adenosquamous carcinoma, 1.4% mucinous adenocarcinomas. Human epidermal growth factor receptor 2 negative group included 56 (81.2%) patients and the positive group had 10 (14.35%) patients. We did not find any statistical difference for the values of SUVmax and tumor-to-liver SUVmax on all histological types of gastric carcinoma on the dual-phase PET scan. High-level SUV1 was found in the HER2 positive group (8.01±3.11) than negative group (6.15±3.76) in early PET/CT imaging (P=0.043) for adenocarcinoma patients. A positive correlation was observed between HER2 and SUV1 in adenocarcinoma patients (r=0.254,P=0.042). An inverse correlation was determined for histological grade with SUV1 (r=-0.29,P=0.048), TLR1 (r=-0.29,P=0.048) and TLR2 (r=-0.324, P=0.03).

Patients with HER2 expression in gastric adenocarcinomas had higher SUVmax values, but no significant difference was found between the groups when the tumor/liver ratio was measured by SUVmax from normal liver parenchyma when background activity was excluded. Signet ring cell carcinoma type and the presence of the signet ring component had no effect on ¹⁸F-FDG uptake.