H. pylori does not cause cancer on infection; it initiates a cascade that runs over decades.The cascade runs: chronic non-atrophic gastritis → atrophic gastritis → intestinal metaplasia → dysplasia → intestinal-type gastric cancer. Each step is probability, not certainty; but each step forward makes reversal harder.
2 · The first two stations are reversible
After H. pylori is eradicated, the first two stations, chronic gastritis and atrophy, can reverse; early intestinal metaplasia may also improve, but on weaker evidence.Good news: the cascade's first two stations (chronic gastritis, atrophy) are reversible after H. pylori eradication. Liang 2024 : atrophy reversal 2.96. Intestinal metaplasia is station three — traditionally the point of no return; the same meta found early IM can also improve (OR 2.41), but that evidence is weaker than for atrophy. Do not fold IM into the first two stations. The mechanism is removing chronic inflammatory drive.
3 · The further, the harder to return
The further along, the harder the return: by dysplasia, eradication can only halt progression, and abnormal clones already present rarely fully regress.Intestinal metaplasia may still improve but evidence is weaker; by dysplasia, eradication only halts progression — existing abnormal clones rarely fully regress. Uemura 2001 prospective cohort: 1246 infected followed 7.8 years, 2.9% developed gastric cancer; 280 uninfected: 0%. One of the strongest causal evidence pieces.
4 · Earlier eradication = more certain benefit
Eradicating before atrophy and intestinal metaplasia appear makes reversal more likely, so do not wait for those stages before treating.Core message: eradication before atrophy and IM is more likely to reverse those stages. Ford 2020: about 72 healthy infected adults treated to prevent one gastric cancer; after endoscopic resection of gastric neoplasia, is 21 (higher baseline risk, so a lower NNT). Earlier eradication is more certain for reversing atrophy; it is not a lower NNT in the hung . This does not mean skip treatment after IM — eradication still lowers progression risk — but do not wait that long.