Objective To investigate the value of ¹⁸F-fluorodeoxyglucose (FDG) PET/CT in the histopathological classification and prognosis of common primary gastric lymphoma (PGL) (diffuse large B-cell lymphoma (DLBCL) and mucosa-associated lymphoid tissue (MALT) lymphoma).

Methods The clinical and imaging data of 83 patients with PGL who underwent ¹⁸F-FDG PET/CT at the Second Xiangya Hospital of Central South University from March 2015 to March 2022 were retrospectively analyzed. The patients included 39 males and 44 females aged 13–78 years old with a median age of 56 (48, 66) years. DLBCL (46 cases) and MALT lymphoma (37 cases) were classified in accordance with histopathological type to compare the clinical characteristics (sex, age, Lugano stage, B symptoms, lactate dehydrogenase level, international prognostic index (IPI), and cell proliferating nuclear antigen Ki-67 (Ki-67) level), imaging features (gastric wall thickness, gastric wall thickening type, lesion site, gastric wall morphology, and extragastric infiltration), and metabolic parameters (maximum standardized uptake value (SUV_max), total lesion glycolysis (TLG)) and metabolic tumor volume (MTV)) of the two types of patients with PGL. Counting data were expressed as frequency and percentage, and comparison between groups was performed by using chi-square test or Fisher's exact probability method. Measurement data conforming to normal distribution were expressed as \bar x\pm s , and comparison between groups was performed by using two independent samples t-test. Measurement data not conforming to normal distribution were expressed as M (Q₁, Q₃), and the Mann-Whitney U test was employed for comparison between groups. Receiver operating characteristic (ROC) curves were applied to analyze the value of metabolic parameters and gastric wall thickness in differentiating DLBCL from MALT lymphoma. The optimal cut-off values for predicting disease progression were calculated using SUV_max, TLG, MTV, gastric wall thickness, and Ki-67. According to these values, classifications were made. The Kaplan-Meier method was utilized for survival analysis. The Log-rank method was used to assess differences between groups, and univariate and multivariate Cox regression analysis was performed for factors that may affect progression-free survival (PFS) time.

Results Patients with DLBCL were more likely to have perigastric invasion, luminal mass, antral involvement, multisite involvement, and the diffuse thickening of the gastric wall than those with MALT lymphoma (58.7% vs. 21.6%, 21.7% vs. 2.7%, 71.7% vs. 35.1%, 54.3% vs. 32.4%, 43.5% vs. 27.0%, χ²=3.99–11.56, all P<0.05). The gastric wall thickness, TLG, and SUV_max of patients with DLBCL were significantly higher than those of patients with MALT lymphoma, and their differences were statistically significant (20.5 (13.0, 32.3) vs. 12.0 (10.0, 16.5) mm, 603.2 (138.8, 1 971.0) g vs. 69.9 (22.3, 208.3) g, (23.4±11.5) vs. (6.6±3.9), Z=−3.72, −4.24, t=−9.30, all P<0.05). ROC curve analysis showed that SUV_max, TLG, and gastric wall thickness had significant differences in their diagnostic power for differentiating MALT lymphoma from DLBCL (AUC=0.915, 0.772, 0.738; all P<0.05). When the critical value was SUV_max=11.95, the sensitivity was 80.4% and the specificity was 91.9%. Kaplan-Meier survival analysis revealed that gastric wall thickness, SUV_max, TLG, and MTV were significantly correlated with PFS rate (χ²=6.98–12.71, all P<0.01). Age, Lugano stage, IPI, Ki-67, and diffuse thickening of the gastric wall were significantly correlated with PFS rate (χ²=4.31–15.11, all P<0.05). Univariate Cox regression analysis demonstrated that gastric wall thickness, SUV_max, TLG, and MTV were the risk factors of PFS time in patients with DLBCL, and the differences of these factors were statistically significant (HR=5.749–8.768, all P<0.05). The type of gastric wall thickening was a risk factor of PFS time in patients with MALT lymphoma, and its difference was statistically significant (HR=8.683, P=0.022). Multivariate Cox regression analysis revealed that SUV_max was an independent risk factor of PFS time in patients with DLBCL, and its difference was statistically significant (HR=9.317, P=0.047).

Conclusions The ¹⁸F-FDG PET/CT imaging of DLBCL and MALT lymphoma has certain characteristics. ¹⁸F-FDG PET/CT metabolic parameters can not only distinguish DLBCL from MALT lymphoma, it can also predict the prognosis of patients with DLBCL.