Immortal time bias exaggerates the effect of metformin on the risk of gastric cancer: A meta-analysis

Big data approach in the field of gastric and colorectal cancer research

Big data is characterized by three attributes: volume, variety,, and velocity. In healthcare setting, big data refers to vast dataset that is electronically stored and managed in an automated manner and has the potential to enhance human health and healthcare system. In this review, gastric cancer (GC) and postcolonoscopy colorectal cancer (PCCRC) will be used to illustrate application of big data approach in the field of gastrointestinal cancer research. Helicobacter pylori (HP) eradication only reduces GC risk by 46% due to preexisting precancerous lesions. Apart from endoscopy surveillance, identifying medications that modify GC risk is another strategy. Population-based cohort studies showed that long-term use of proton pump inhibitors (PPIs) associated with higher GC risk after HP eradication, while aspirin and statins associated with lower risk. While diabetes mellitus conferred 73% higher GC risk, metformin use associated with 51% lower risk, effect of which was independent of glycemic control. Nonetheless, nonsteroidal anti-inflammatory drugs (NA-NSAIDs) are not associated with lower GC risk. CRC can still occur after initial colonoscopy in which no cancer was detected (i.e. PCCRC). Between 2005 and 2013, the rate of interval-type PCCRC-3y (defined as CRC diagnosed between 6 and 36 months of index colonoscopy which was negative for CRC) was 7.9% in Hong Kong, with >80% being distal cancers and higher cancer-specific mortality compared with detected CRC. Certain clinical and endoscopy-related factors were associated with PCCRC-3 risk. Medications shown to have chemopreventive effects on PCCRC include statins, NA-NSAIDs, and angiotensin-converting enzyme inhibitors/angiotensin receptor blockers.

Chinese national clinical practice guidelines on the prevention, diagnosis, and treatment of early gastric cancer

BACKGROUND

Gastric cancer is one of the most common malignant tumors in the digestive system in China. Few comprehensive practice guidelines for early gastric cancer in China are currently available. Therefore, we created the Chinese national clinical practice guideline for the prevention, diagnosis, and treatment of early gastric cancer.

METHODS

This clinical practice guideline (CPG) was developed in accordance with the World Health Organization's recommended process and with the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) in assessing evidence quality. We used the Evidence to Decision framework to formulate clinical recommendations to minimize bias and increase transparency in the CPG development process. We used the Reporting Items for practice Guidelines in HealThcare (RIGHT) statement and the Appraisal of Guidelines for Research and Evaluation II (AGREE II) as reporting and conduct guidelines to ensure completeness and transparency of the CPG.

RESULTS

This CPG contains 40 recommendations regarding the prevention, screening, diagnosis, treatment, and follow-up of early gastric cancer based on available clinical studies and guidelines. We provide recommendations for the timing of Helicobacter pylori eradication, screening populations for early gastric cancer, indications for endoscopic resection and surgical gastrectomy, follow-up interval after treatment, and other recommendations.

CONCLUSIONS

This CPG can lead to optimum care for patients and populations by providing up-to-date medical information. We intend this CPG for widespread adoption to increase the standard of prevention, screening, diagnosis, treatment, and follow-up of early gastric cancer; thereby, contributing to improving national health care and patient quality of life.

Diabetes Mellitus and Gastric Cancer: Correlation and Potential Mechanisms

This review summarizes the correlation between diabetes mellitus (DM) and gastric cancer (GC) from the perspectives of epidemiology, drug use, and potential mechanisms. The association between DM and GC is inconclusive, and the positive direction of the association reported in most published meta-analyses suggests that DM may be an independent risk factor for GC. Many clinical investigations have shown that people with DM and GC who undergo gastrectomy may have better glycemic control. The potential link between DM and GC may involve the interaction of multiple common risk factors, such as obesity, hyperglycemia and hyperinsulinemia, H. pylori infection, and the use of metformin. Although in vitro and in vivo data support that H. pylori infection status and metformin can influence GC risk in DM patients, there are conflicting results. Patient survival outcomes are influenced by multiple factors, so further research is needed to identify the patients who may benefit.

Chronic metformin intake and gastric cancer: A pooled analysis within the Stomach cancer Pooling (StoP) Project

INTRODUCTION

The association between chronic use of metformin and risk of gastric cancer (GC) has been investigated with contradicting results. We aimed to study the association between chronic use of metformin and GC by using data from the Stomach cancer Pooling (StoP) Project, an epidemiological consortium of case-control studies on GC.

METHODS

Data from three studies of the StoP Project with available information on metformin intake were analyzed. Multivariable logistic regression models were used to estimate study-specific odds ratios (ORs) and 95% confidence intervals (CIs) for the association between chronic use of metformin and GC risk. Analyses were adjusted for sex, age, socioeconomic status, body mass index, smoking status, alcohol drinking status, and history of diabetes. Study-specific ORs and 95% CIs were then pooled with a random-effects model. The dose-response relationship between the duration of metformin intake and GC was assessed with a one-stage logistic model, and the duration of intake was modelled using second-order fractional polynomials.

RESULTS

The OR of GC in metformin users versus non-users was 1.01 (95% CI=0.61, 1.67). The association between metformin and GC did not change among different strata of study participants' characteristics or when restricting the analyses to those with a history of diabetes. The dose-response analysis showed a slightly reducing trend in the OR of GC and a borderline significant association with increasing duration of metformin intake.

CONCLUSIONS

The results of our study do not clearly support an association between chronic use of metformin and GC, warranting further research.

Metformin use is not associated with reduced risk of older onset inflammatory bowel disease: a Danish nationwide population-based study

BACKGROUND

Metformin has pleiotropic effects including anti-inflammatory properties and effects on the gut microbiome. It is primarily used in the older population, where the occurrence of inflammatory bowel disease (IBD) is increasing. The aim of this study was to examine whether metformin protects against development of IBD.

METHODS

In the setting of a Danish nationwide population-based cohort, we conducted a nested case-control study using a new-user active comparator design. For each patient with IBD, we selected 10 IBD-free individuals matched on age, sex, and duration of follow-up. Conditional logistic regression was used to estimate odds ratios (ORs) of IBD. Adjustment included educational level, other immune-mediated inflammatory diseases, and use of dipeptidyl peptidase (DPP)-4 inhibitors and statins.

RESULTS

Among 302,863 IBD-free new users of oral glucose-lowering drugs, we identified 1271 patients who developed IBD and 12,676 matched IBD-free individuals. Mean age at IBD diagnosis was 66 (SD, 11) years. We found no association between ever use of metformin and risk of IBD, Crohn's disease or ulcerative colitis, adjusted OR 0.95 (95% CI 0.78-1.15), 0.87 (95% CI 0.60-1.26), and 1.04 (95% CI 0.83-1.31), respectively. Neither was the cumulative dose of metformin or the treatment duration with metformin associated with risk of IBD.

CONCLUSIONS

In this population-based study, we report that despite anti-inflammatory effects and a notable impact on the gut microbiome, metformin use is not associated with reduced risk of older onset IBD.

Metformin and survival of women with breast cancer: A meta-analysis of randomized controlled trials

WHAT IS KNOWN AND OBJECTIVE

Metformin has been suggested to confer anticancer efficacy. However, it remains uncertain whether additional use of metformin could improve survival of women with breast cancer. We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the influence of metformin on survival outcome in women with breast cancer.

METHODS

Relevant RCTs were obtained by search of PubMed, Embase and Cochrane's Library databases from inception to 15 May 2021. A random-effects model incorporating the potential publication bias was used to pool the results.

RESULTS AND DISCUSSION

Five phase II RCTs including 396 non-diabetic women with breast cancer were included in the meta-analysis. Pooled results showed that additional use of metformin was not associated with improved progression-free survival (PFS, hazard ratio [HR]: 1.00, 95% confidence interval [CI]: 0.70 to 1.43, p = 0.98; I²  = 32%) or overall survival (OS, HR: 1.00, 95% CI: 0.71 to 1.39, p = 0.98; I²  = 0%). Sensitivity analysis by excluding one study at a time showed consistent results (HR for PFS: 0.91 to 1.14, p all >0.05; HR for OS: 0.88 to 1.21, P all >0.05).

WHAT IS NEW AND CONCLUSION

Current evidence from phase II clinical trials does not support that additional use of metformin could improve the survival outcome in women with breast cancer.

Chemopreventive Effect of Metformin on Gastric Cancer Development

Although Helicobacterpylori infection is the most important causative factor for gastric cancer (GC), H. pylori eradication alone does not completely eliminate the GC risk. In addition to H. pylori eradication, other risk factors for GC should be identified and targeted. Diabetes mellitus (DM) confers a 20% increased risk of GC, which could be mediated via several biological mechanisms including the stimulation of cell proliferation via hyperinsulinemia and increased insulin-growth factor production, the promotion of angiogenesis, and DNA damage. With a current global prevalence of 9.3% and a predicted rise to 10.2% by 2030, DM could contribute substantially to the burden of GC cases worldwide. Emerging evidence showed that metformin possesses chemopreventive effects via both direct (e.g., adenosine monophosphate-activated protein kinase activation and subsequent inhibition of the mammalian target of rapamycin pathway) and indirect (e.g., modulation of the interaction between tumor cells and their microenvironment and gut microbiota) pathways. A recent meta-analysis of observational studies showed that metformin use was associated with 24% lower GC risk. However, many available observational studies related to metformin effects suffered from biases including the failure to adjust for the H. pylori infection status and serial glycemic control and time-related biases. Future prospective studies addressing these pitfalls are needed.