A retrospective analysis of patient data revealed that people with Helicobacter pylori strains carrying a certain gene were about half as likely to develop adenocarcinoma of the esophagus as people who didn't have it. Strains of H. pylori carrying the CagA gene may reduce gastric acid production, reducing acid reflux to the esophagus. The bacteria may also help by decreasing production of a gastric hormone that stimulates appetite. This could help prevent obesity, a prime risk factor for esophageal adenocarcinoma.
Researchers analyzed results from 19 published studies concerning the link between H. pylori and esophageal cancers. They conclude that "[t]he prominent decline of H. pylori colonization in the past few decades may be partly responsible for the recent increase in esophageal adenocarcinoma incidence in Western countries."
Source: Islami F, Kamangar F. Helicobacter pylori and esophageal cancer risk: a meta-analysis. Cancer Prev Res. 2008;1(5):329-338.