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Letter
Response to letter to the editor by Moayyedi et al
  1. Ka-Shing Cheung,
  2. Wai Keung Leung
  1. Department of Medicine, University of Hong Kong, Hong Kong, Hong Kong
  1. Correspondence to Dr Wai Keung Leung, Departmenyt of Medicine, Queen Mary Hospital, Hong Kong, Hong Kong; waikleung{at}hku.hk

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We thank Moayyedi et al 1 for their letter on our recent study investigating proton pump inhibitors (PPIs) on gastric cancer (GC) risk after Helicobacter pylori (HP) eradication.2 Although the association detected by an observational study may not mean causation, the possibility of causality can be strengthened by fulfilling the Bradford Hill criteria. In our study, these include strength (HR: 2.43), specificity (stomach is the only organ that PPIs may impose a cancer risk), temporality (all GC cases developed after triple therapy), biological gradient (dose and duration response relationship shown), plausibility (worsening of preneoplastic gastric changes and bacterial overgrowth under profound acid suppression), experiment (as illustrated in animal model studies) and analogy (achlorhydria due to autoimmune gastritis causes GC).

Concerns were raised over inadequate adjustment for socioeconomic status and comorbidities. Hong Kong is a highly urbanised city with excellent sanitation and easily accessible …

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