Helicobacter pylori-Associated Atrophic Gastritis and Risk of Gastric and Breast Cancer: A Prospective Cohort Study in Thailand.

BACKGROUND: Chronic atrophic gastritis (CAG), primarily driven by Helicobacter pylori infection, is a well-established precursor to gastric cancer. However, its association with extragastric malignancies remains poorly understood, especially in high-prevalence, resource-limited settings. We aimed to evaluate the risk of gastric and extragastric cancers in Thai patients with CAG. METHODS: This hospital-based prospective cohort study included 1,252 Thai adults with histologically confirmed CAG between 2012 and 2017. Participants were stratified by H. pylori status. Incident cancers were identified via linkage with the national cancer registry through 2023. Cancer risks were estimated using Kaplan-Meier survival analysis and Cox proportional hazards models, adjusting for demographic, behavioral, and familial factors. RESULT: Over a median follow‑up of 7.9 years (9,679 person‑years), 44 participants developed cancer, corresponding to an incidence of 455 per 100,000 person‑years. Gastric cancer (n = 14) and breast cancer (n = 16) were the most frequent malignancies. H. pylori-associated atrophic gastritis (HPAG) was significantly associated with increased risks of gastric cancer (HR 2.03; 95% CI: 1.25-3.26; p = 0.012) and breast cancer (HR 7.35; 95% CI: 2.08-17.13; p < 0.001) compared with non‑HPAG patients. No significant associations were observed for other cancer types. CONCLUSION: HPAG is a primary driver of gastric cancer risk and is associated with a significantly elevated risk of breast cancer in this cohort. These findings underscore the importance of early detection and eradication of H. pylori before irreversible glandular loss. While the breast cancer association is exploratory, it suggests systemic oncogenic effects of chronic infection, warranting prioritized gastric surveillance and consideration for breast cancer screening in female HPAG patients.