Originally Posted by goodymehrin
why does achlorhydria increases the risk for developing adenocarcinoma?
It's not the decrease in stomach acid (achlorhydria) per se that increases the risk, it's the reason behind the achlorhydria.
What's really happening is chronic inflammation for some reason that leads to atrophic gastritis. This can be the result of an autoimmune process that attacks the parietal cells, or from H Pylori infection. Either way, you get this chronic inflammation and destruction of parietal cells.
A general rule in pathology is that whenever you increase inflammation and cell turnover, you increase the risk of cancer. That holds true here. It also happens that this same inflammation and cell destruction leads to decreased acid production.