Abstract
Chronic Helicobacter pylori (Hp) infection is considered to be the single most important risk factor for the development of gastric adenocarcinoma in humans, which is a leading cause of cancer-related death worldwide. Nonetheless, Hp infection does not always progress to malignancy, and, gastric adenocarcinoma can occur in the absence of detectable Hp carriage, highlighting the complex and multifactorial nature of gastric cancer. Here we review known contributors to gastric malignancy, including Hp virulence factors, featuring the vacuolating cytotoxin (VacA), the cytotoxin-associated gene A (CagA), and other bacterial components that promote chemotaxis, colonization, and the establishment of chronic inflammation. In addition, we discuss host factors including sex, age, and genetic polymorphisms associated with host inflammation. Moreover, we consider environmental variables that influence cancer risk, such as nutritional status, socio-economic status, and smoking. In addition to these relatively well-studied contributors to gastric cancer risk, the resident gastric microflora in humans have more recently been proposed as an additional risk factor for disease progression in Hp-infected individuals. Molecular approaches for microbe identification have revealed differences in the gastric microbiota composition between cancer and non-cancerous patients, as well as infected and uninfected individuals. Although the reasons underlying differences in microbial community structures are not entirely understood, gastric atrophy and hypochlorhydria that accompany chronic Hp infection may be a critical driver of gastric dysbiosis that promote colonization of microbes that contribute to increased risk of malignancy. However, definitive evidence that the gastric microbiota influences the emergence of gastric cancer does not exist. In summary, while controversial and unresolved, the importance of the gastric microbiota as a risk factor for gastric malignancy is a vital area of current research.