Proton Pump Inhibitors and Gastric Cancer Risk: A Systematic Review

The systematic review and evidence synthesis you referred to evaluates the long-debated association between proton pump inhibitor (PPI) use and gastric cancer risk. It aims to assess potential causality through a life course epidemiology framework. Here's a detailed summary of the findings:

### **Overview of the Evidence**

The review includes a comprehensive analysis of studies up to October 2024, examining the relationship between PPI use and gastric cancer risk in humans. The evidence base consists of:

• **33 original studies**
• **21 meta-analyses**
• **Three umbrella meta-analyses**
• **One individual patient data meta-analysis**
• **One Markov model**

### **Key Findings**

1. **Association Between PPI Use and Gastric Cancer Risk**:

• Across the studies, PPIs were consistently associated with an increased risk of gastric cancer.
• Out of 21 meta-analyses, 20 reported pooled relative risks (RRs) ranging from approximately **1.3 to 2.9**, indicating a significant association.

2. **Challenges in Interpretation**:

• **Confounding by indication**: Patients prescribed PPIs often have underlying conditions that may themselves increase gastric cancer risk.
• **Reverse causation**: Gastric cancer symptoms may lead to PPI prescriptions, rather than PPIs causing cancer.
• **Insufficient lag time**: Many studies did not account for the time required for cancer to develop.
• **Helicobacter pylori infection and eradication therapy**: It was difficult to separate the effects of PPIs from those of H. pylori eradication therapies, which are also linked to gastric cancer risk.

3. **Consistency Across Study Designs**:

• Despite methodological challenges, the association between PPI use and gastric cancer risk remained consistent across different study designs, populations, and analytical approaches.

### **Life Course Epidemiology Framework**

The authors propose a "sensitive period" model, suggesting that exposure to PPIs during early life, childhood, or young adulthood may pose greater long-term gastric cancer risk compared to exposure later in life. Supporting evidence includes:

• Exploratory analyses of Swedish cancer incidence data showing:
• Declining overall gastric cancer rates since 1970.
• Increasing incidence among younger men (<40 years) starting in the early 2000s, which aligns with widespread PPI use and Helicobacter pylori eradication strategies.

### **Implications for Prescribing Practices**

• **Older Adults**: In older adults with clear indications for PPI use (e.g., gastroesophageal reflux disease or peptic ulcers), the gastric cancer risk may be limited.
• **Younger Populations**: The widespread and often unwarranted long-term use of PPIs in younger populations raises concern, given the potential long-term risk of gastric cancer.
• **Caution in Prescribing**:
• The study underscores the need for a more cautious, evidence-based approach to prescribing PPIs.
• Avoiding unnecessary long-term PPI use, especially in younger individuals, is recommended.

### **Conclusion**

This systematic review highlights a consistent association between PPI use and increased gastric cancer risk, particularly when exposure occurs during sensitive periods of life. While the risk may be limited in older adults with clear indications for PPI use, the findings suggest that unwarranted long-term use—especially in younger populations—should be minimized. Healthcare providers are encouraged to adopt a more cautious and evidence-based prescribing approach to mitigate potential risks.

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