Boston—The possible association between metformin use and reduction in the risk of cancer has been repeatedly considered, but results have been anything but consistent.
That is why a new study, conducted by the largest healthcare system in the United States, is so important. The Veterans Health Administration treats more patients with diabetes than any other healthcare system in the country, and the vast majority of those patients take metformin. As a result, it is in a good position to help determine if biguanide actually reduces cancer risk.
The researchers at the Boston University School of Medicine and the Veterans Affairs (VA) Boston Healthcare System conducted a study of veterans aged 55 years and older with diabetes who started treatment with metformin or sulfonylurea (SU) between 2001 and 2012. The participants maintained regular use of the diabetes medications, remained cancer-free, and did not take any other diabetes drugs. Included in the analysis were 60,477 veterans who initiated treatment with metformin and 28,237 who started on SU.
The results were presented at the 64th American Society of Hematology Annual Meeting in New Orleans, Louisiana.
Over a mean follow-up of 4.2 years, 7,383 of these veterans with diabetes developed cancer. The researchers determined that 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 older). The results indicated that the incidence of any cancer was 19% lower among 55- to 64-year-olds who took metformin compared with their peers who took SUs (HR 0.79, 95% CI 0.63-0.98). Among those aged 65 to 74 years, 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 authors reported that the use of metformin was associated with an even greater reduction in the risk of hematological cancers for the youngest two age groups—32% reduction for those aged 55 to 64 years (HR 0.68, 95% CI 0.54-0.87) and 21% reduction for patients aged 65 to 74 years (HR 0.93; 95% CI: 0.69-1.25). No difference in cancer risk was evident in the older group.
“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 researchers concluded.
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