Salivary Fusobacterium nucleatum serves as a potential diagnostic biomarker for gastric cancer

BACKGROUND As one of the most common tumors, gastric cancer (GC) has a high mortality rate, since current examination approaches cannot achieve early diagnosis. Fusobacterium nucleatum (Fn) primarily colonized in the oral cavity, has been reported to be involved in the development of gastrointestinal tumor. Until now, little is known about the relationship between salivary Fn and GC. AIM To determine whether salivary Fn could be a biomarker to diagnose GC and explore the influence of Fn on GC cells. METHODS The abundance of Fn in saliva was quantified by droplet digital polymerase chain reaction in 120 GC patients, 31 atrophic gastritis (AG) patients, 35 non-AG (NAG) patients, 26 gastric polyp (GP) patients, and 20 normal controls (NC) from Qilu Hospital of Shandong University from January 2019 to December 2020. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic value of Fn as well as traditional serum tumor markers, including carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9, and CA72-4. Transwell assay and wound-healing assay were conducted to assess the influence of Fn infection on GC cells. The expression of epithelial-mesenchymal transition (EMT) markers was detected using western blot assay. RESULTS We found that the level of salivary Fn in GC patients was significantly increased compared with those in AG, NAG, and GP patients and NC (P < 0.001). ROC curve analysis showed a favorable capability of Fn (73.33% sensitivity; 82.14% specificity; area under the curve: 0.813) in GC diagnosis, which was superior to that of CEA, CA19-9, CA72-4, ferritin, and sialic acid. The Fn level in saliva of GC patients was increased as the TNM stage increased. GC patients with lymph node metastasis had higher Fn levels than those without metastasis. Both transwell and wound-healing assays indicated that Fn infection promoted the migration and invasion of GC cells. Western blot analysis showed that Fn infection decreased the expression of E-cadherin and increased the expressions of N-cadherin, vimentin, and snail. CONCLUSION Fn abundance in saliva could be used as a promising biomarker to diagnose GC, and Fn infection could promote GC metastasis by accelerating the EMT process.