Adherence to metformin translates to bone cancer protection in older men

Type 2 diabetes (T2D) patients who adhere to metformin treatment appear to be at lower risk of developing bone cancer, and this protective effect is seen exclusively among older men, a study reports.

The study used data from Taiwan's National Health Insurance and included 673,532 newly diagnosed T2D patients who were prescribed glucose-lowering drugs for two or more times. Metformin use was identified based on prescriptions within the initial 12 months.

Of the patients, 453,532 initiated metformin and 220,000 did not. Over a follow-up of up to 12 years, bone cancer incidence rates were 10.56 and 12.90 per 100,000 person-years in the metformin initiator and noninitiator groups, respectively, in the intention-to-treat analysis.

Multivariable Cox regression analysis revealed that metformin use reduced the risk of incident bone cancer by 17 percent (hazard ratio [HR], 0.830, 95 percent confidence interval [CI], 0.686–1.004; p=0.0551).

Results of the per-protocol analysis followed the same pattern. The incidence rate of bone cancer was lower among metformin initiators than among noninitiators (7.58 vs 11.77 per 100,000 person-years), with a corresponding HR of 0.615 (95 percent CI, 0.468–0.808; p=0.0005).

However, subgroup analyses defined by sex and age (<60 and ≥60 years) showed that the protective effect of metformin use on bone cancer was only present in men aged ≥60 years in the per-protocol analysis.