Despite some evidence to the contrary, metformin does not appear to decrease the risk for cancer in patients with type 2 diabetes, according to data published in Diabetes Care. Larger, randomized, controlled trials, however, are needed before researchers can definitely determine that there is no association.
In a retrospective observational study using the German Disease Analyzer database, hazard ratios (HRs) for cancer were 1.09 (95% CI, 0.87-1.36) for sulfonylurea monotherapy, 1.14 (95% CI, 0.85-1.55) for insulin monotherapy and 0.94 (95% CI, 0.67-1.33) for other diabetes medications vs. metformin monotherapy.
The researchers also noted similar results for comparison of first diabetes medications.
Multivariable adjusted models were used for analysis, and the study sample was composed of 22,256 patients with type 2 diabetes from general practices throughout Germany. Median follow-up was 4.8 years, during which 1,446 (6.4%) developed cancer. Either monotherapies or first diabetes medications as drug exposure, users of sulfonylurea, insulin or other antidiabetes medications were then compared with metformin users in Cox regression analyses.
The researchers concluded that “taking into account potential time-related biases, no reduced cancer risk was found in metformin users,” although further observational studies and controlled trials are needed.
Several meta-analyses of observational studies suggested that metformin use reduces cancer risk in type 2 diabetes, but this result was not confirmed in few available randomized controlled trials. Further, many observational studies on metformin and cancer were potentially afflicted with time-related bias.
Researchers in this study published in Diabetes Care sought to avoid this bias when comparing cancer incidence in users of sulfonylurea, insulin and other diabetes medications, respectively, with cancer incidence in metformin users.
These results offer further evidence on the metformin–reduced cancer risk connection.