Gastric cancer and the microbiome

The human body harbours more than 10¹⁹ microbial species, a majority of which reside in the alimentary tract. Alterations in the organ specific microbiome have been associated with carcinogenesis, especially in colorectal cancer. Helicobacter pylori (H. pylori) has been known to be involved in gastric tumorigenesis for almost 2 decades. The ability of H. pylori to evade host immune responses and induce genomic aberrations via a gamut of virulence factors such as VacA and CagA probably contributes to its significant role in gastric carcinogenesis. However, recent studies have determined that H. pylori is not the sole microbe found in the gastric milieu. Moreover, observed differences in the microbial composition of the gastric milieu between healthy, gastritis afflicted and cancer patients point towards a probable role of these microbes in pathogenesis of gastric diseases. This review aims to summarize the current understanding of the gastric microbiome and its role in influencing gastric carcinogenesis.