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Sulfonylureas, Insulin, and Metformin Cancer Risks for Patients with Type 2 Diabetes

Can metformin reduce the risk of cancer for those with type 2 diabetes?…

In previous studies, metformin has been shown to decrease the risk of cancer in type 2 diabetes. A recent meta-analysis showed a 34% reduction in the incidence of any cancer and a 33% reduction in cancer mortality; however, the studies are prone to bias and failed to confirm the results of observational studies.

In this study, German researchers focused on avoiding biases from other prior analyses, comparing cancer cases using sulfonylurea, insulin, and other diabetes medications with cancer cases using metformin.

The researchers included 22,556 patients with type 2 diabetes from the German Disease Analyzer database. There were two comparisons in the study: intention-to-treat (compared patients with sulfonylurea or insulin or other medications except metformin as their first diabetes medication with patients with metformin as their first diabetes medication) and monotherapies (compared patients with a monotherapy of sulfonylurea, insulin, or other medications except metformin with patients with a metformin monotherapy).

When comparing the first therapies, the studies detected the risk reductions in metformin users: 21% (sulfonylurea vs. metformin), 32% (insulin vs. metformin), and 26% (other diabetes drugs vs. metformin). For monotherapies, risk reductions were detected as follows: 33% (sulfonylurea vs. metformin), 41% (insulin vs. metformin), and 38% (other diabetes drugs vs. metformin).

Approximately 1,446 (6.4%) patients developed cancer during 4.8 years of median follow-up. Collecting all the data from all sites, hazard ratios 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 compared with metformin monotherapy.

The researchers concluded, “In a retrospective database analysis, taking into account potential time-related biases, no reduced cancer risk was found in metformin users. To clarify the association between diabetes medication and cancer risk, further well-designed observational studies and RCTs are needed.”

Practice Pearls:

  • In this study, the data showed that risk of cancer was not decreased in the use of metformin in comparison to other diabetes drugs.
  • Patients with metformin as first diabetes medication had fewer microvascular complications, more hypertension, dyslipidemia and obesity than patients using other drugs as their first diabetes medication.
  • Metformin was mostly used as first line medication. In contrast, sulfonylurea and insulin were used as second or third line medications. Physicians should always discuss the risks and benefits of these diabetes medications with their patients.

Bernd Kowall. Are Sulfonylurea and Insulin therapies associated with a larger risk of cancer than metformin therapy? A retrospective database analysis. Diabetes Care. Jan 2015; 38: 59-65.