How Scientific Dogma Delayed The Discovery of The Bacterium Behind 5% of All Cancers

One bacterium causes roughly 1 in 20 cancer cases worldwide. It’s the most cancer-causing pathogen we’ve found—and the main cause of peptic ulcers. Its discovery overturned an ironclad medical dogma that the stomach was sterile.

Despite infecting about half of humanity, Helicobacter pylori wasn’t discovered until 1979 and shown to cause gastritis and peptic ulcer disease in the early 1980s. Why did it evade detection for so long—and what finally broke through the consensus?

I went to Perth, Australia—where H. pylori was first discovered—to chat with Barry Marshall, gastroenterologist and co-recipient (with Robin Warren) of the 2005 Nobel Prize in Physiology or Medicine for discovering H. pylori and proving that it causes gastritis and peptic ulcer disease. Marshall famously infected himself with the bacterium to demonstrate causality and later helped develop clinical diagnostics like the urea breath test, which we demo live in the episode.