Metformin Linked to Decreased Risk of Cancer

Metformin use may decrease the risk of cancer, but more research is needed to confirm this finding, according to researchers.

The researchers conducted a meta-analysis and found that, in some studies, metformin use was associated with a decreased risk of cancer overall and a decrease in gastrointestinal, genitourinary, gynecologic, and other cancers. The researchers reported these findings in the Journal of the National Cancer Institute.

The meta-analysis included 166 studies with information on cancer incidence and metformin use. There were 85 retrospective cohort studies, 55 case-control studies, 21 prospective cohort studies, 2 cross-sectional studies, 1 randomized controlled trial, and 2 studies that included estimates for both retrospective cohort and nested case-control studies.

Metformin use was associated with a reduction in overall cancer incidence in the prospective studies (relative risk [RR], 0.65; 95% CI, 0.37-0.93) and case-control studies (RR, 0.55; 95% CI, 0.30-0.80) but not in the cross-sectional studies (RR, 0.96; 95% CI, 0.67-1.24) or retrospective cohort studies (RR, 0.86; 95% CI, 0.70-1.03).

When the researchers looked at specific cancers, they found that metformin use was associated with a decrease in colorectal cancer incidence in case-control studies (RR, 0.71; 95% CI, 0.50-0.92), prospective cohort studies (RR, 0.37; 95% CI, 0.29-0.45), and retrospective cohort studies (RR, 0.85; 95% CI, 0.75-0.96) but not in nested case-control studies (RR, 0.92; 95% CI, 0.84-1.01).

Metformin use was associated with a lower incidence of liver cancer in case-control studies (RR, 0.54; 95% CI, 0.29-0.79), nested case-control studies (RR, 0.70; 95% CI, 0.63-0.78), and retrospective cohort studies (RR, 0.73; 95% CI, 0.61-0.85).

Metformin use was also associated with a reduction in prostate cancer incidence in case-control studies (RR, 0.91; 95% CI, 0.88-0.94) and prospective cohort studies (RR, 0.80; 95% CI, 0.61-0.99) but not in nested case-control studies (RR, 1.02; 95% CI, 0.78-1.25) or retrospective cohort studies (RR, 0.85; 95% CI, 0.71-1.00).

For other cancers, the researchers did not stratify results by study design due to a limited number of studies for each cancer type. In these analyses, metformin use was associated with a reduced incidence of:

• Bladder cancer (RR, 0.70; 95% CI, 0.56-0.83)
• Cervical cancer (RR, 0.68; 95% CI, 0.49-0.87)
• Esophageal cancer (RR, 0.68; 95% CI, 0.50-0.86)
• Gastric cancer (RR, 0.76; 95% CI, 0.63-0.89)
• Head and neck/oral cancers (RR, 0.58; 95% CI, 0.45-0.72)
• Lung cancer (RR, 0.88; 95% CI, 0.76-0.99)
• Ovarian cancer (RR, 0.53; 95% CI, 0.21-0.85)
• Thyroid cancer (RR, 0.74; 95% CI, 0.51-0.97).

The researchers noted that there were no significant associations between metformin use and an increased risk of any cancer.

They also pointed out that many of the cancers for which metformin appeared to have a protective effect are associated with type 2 diabetes mellitus (T2DM), so metformin may provide a direct preventative cancer benefit or an indirect benefit by controlling T2DM.

“Since the primary indication of metformin prescription is a T2DM diagnosis, both the control populations and experimental populations in this study were typically composed of individuals diagnosed with diabetes,” the researchers wrote. “Thus, while we have gained insight about metformin use and cancer prevention, further studies are needed to clarify the relationship between metformin and cancer risk in non-diabetic populations.”

Disclosures: One study author is an associate editor of the Journal of the National Cancer Institute. Please see the original reference for a full list of disclosures.

This article originally appeared on Cancer Therapy Advisor