In 1994, Helicobacter pylori was declared a
type 1 carcinogen—a definite cause of human cancer—by the International
Agency for Research on Cancer (IARC).1 This
conclusion, which was based largely on epidemiological data that were later
substantiated,2 left behind unsettling questions.
First, some latent concern lingered that H pylori was
merely a marker for other exposures. Despite subsequent studies in animals,
humans, and tissue cultures indicating plausible mechanisms for H pylori–induced carcinogenesis, naysayers have clung to the
small, residual probability that H pylori is merely
a confounder for the true cause of disease. Because H pylori infection is so closely linked to socioeconomic status, such confounders
are not difficult to find.
Parsonnet J, Forman D. Helicobacter pylori Infection and Gastric Cancer—For Want of More Outcomes. JAMA. 2004;291(2):244–245. doi:10.1001/jama.291.2.244