BOSTON — Over the last decade, a number of studies have examined a possible association between metformin use and reduction in the risk of cancer, with contradictory results. A very large study of veterans previously found an association between metformin use and reduced risk of liver cancer, but not other solid cancers. One recent study indicated the drug may reduce the risk of colorectal cancer, while others have found no association.
As the VHA treats more patients with diabetes than any other healthcare system in the United States, and many of those patients take metformin, determining whether the biguanide reduces cancer risk is of keen interest to the VA.
In conjunction with physicians at Boston University School of Medicine, researchers at the VA Boston Healthcare System conducted a study of veterans aged 55 and older with diabetes who started treatment with metformin or sulfonylurea (SU) between 2001 and 2012 and had data through a two-year washout, period during which they maintained regular use of the diabetes medication, remained cancer free, and did not take any other diabetes drugs.
The team identified 60,477 veterans who initiated treatment with metformin and 28,237 who started on SU. With a mean follow-up of 4.2 years, 7,383 of these veterans with diabetes developed cancer. The rate among metformin users was 17.5 per 1,000 person years, while the rate among SU users was 24.5 per 1,000 person years.
Because the risk of cancer increases substantially with age, the researchers then stratified the model by age group (55-64, 65-74 and 75 years or more). The incidence of any cancer was 19% lower among 55- to 64-year-olds who took metformin compared to their peers who took SUs (HR 0.79, 95% CI 0.63-0.98). Among those 65 to 74 years of age, the reduction in cancer risk was 13% for the metformin group (HR 0.87, 95% CI 0.81-0.94). There was no significant difference between the two groups in the oldest cohort.
The use of metformin was associated with an even greater reduction in the risk of hematological cancers for the youngest two age groups with a 32% reduction for those 55-64 (HR 0.68, 95% CI 0.54-0.87) and 21% reduction for patients 65-74 (HR 0.93, 95% CI 0.69-1.25). Again, the oldest group showed no difference in cancer risk.
“Our findings make more urgent the need for randomized controlled trials to determine the potential of metformin in primary prevention of cancer in both solid and liquid tumors, as well as further studies into the mechanism of metformin’s anti-cancer effects,” the team said.
- Abdalla M, Dumontier C, Orkaby A, Cho K, Charest B, Preis S, Driver JA. Metformin Use and Incidence of Cancer: A Large Retrospective Cohort Study of U.S. Veterans. Abstract 4938. 2022 ASH Annual Meeting. Dec. 12, 2022.