MedWire News: Infection with the stomach ulcer-causing bug Helicobacter pylori may protect against the development of a type of oesophageal cancer called adenocarcinoma, a review of published studies suggests.

Dr Farin Kamangar, from the National Cancer Institute in Bethesda, Maryland, USA, and Dr Farhad Islami, from the University of Tehran in Iran, explain that Helicobacter pylori infection is very common, and that humans have been living with the bacterium for more than 60,000 years.

However, research conducted over the past few decades has shown that infection with the bacterium, particularly strains carrying the CagA gene, is associated with an increased risk of peptic ulcers and stomach cancer.

But they add that Helicobacter pylori’s long history of co-existence with humans suggests it may have some beneficial effects.

Indeed, statistics show that, as Helicobacter pylori infection rates have fallen in the developed world alongside advancements in sanitation and antibiotic use, the number of people developing oesophageal adenocarcinoma has increased significantly.

Once rare, oesophageal adenocarcinoma now constitutes approximately half of all oesophageal cancers diagnosed in countries such as the UK and USA, statistics show.

To investigate whether infection with Helicobacter pylori is associated with a reduced risk of oesophageal adenocarcinoma, Drs Kamangar and Islami assessed the results of 19 published studies that examined the association.

Analysis of the pooled results reveals that people infected with Helicobacter pylori strains carrying the CagA gene are nearly 50% less likely to develop oesophageal adenocarcinoma than uninfected people.

Commenting on the findings, Dr Kamangar said: "CagA- positive strains of Helicobacter pylori may decrease the risk of adenocarcinoma by reducing acid production in the stomach and, therefore, reducing acid reflux to the oesophagus.

"It may also work by decreasing the production of the hormone ghrelin, which is secreted from the stomach to stimulate appetite. A reduction in the level of ghrelin may lead to lower rates of obesity, an important risk factor for adenocarcinoma."

The research will be published in a forthcoming issue of the journal Cancer Prevention Research.