Metformin Increases Survival Rate in Type 2 Diabetes after Incident Cancer Diagnosis

Metformin molecule isolated on whiteIt’s known that having type 2 diabetes increases a patient’s risk of developing certain types of cancer; it also reduces survival time following diagnosis.

Researchers looked at this hypothesis related to type 2 diabetes and cancer:  In people with type 2 diabetes, is survival reduced following diagnosis of a solid-tumor cancer?  And does metformin treatment influence survival?

The results of their study were published online ahead of print on January 20, 2012; they will appear in the journal Diabetes Care.  The article is “Mortality After Incident Cancer in People With and Without Type 2 Diabetes:  Impact of metformin on survival.”

For this retrospective cohort study, the researchers gathered data from > 350 United Kingdom primary care practices.  They identified everyone—with or without type 2 diabetes—who developed a first tumor sometime after January 1990; their records were then followed to December 2009.

There were 112,408 patients included in the study; 8,392 (7.5%) of them had type 2 diabetes.

Those patients with diabetes were further stratified according to treatment regimen.

To examine mortality, Cox proportional hazards models were used; these aided the researchers in comparing all-cause mortality from all cancers to mortality from specific cancers.

The study found that in those patients with diabetes, cancer mortality was increased, compared to those who did not have diabetes (hazard ratio 1.09 [95% CI; 1.06-1.13]).

In regards to specific types of cancer in people with type 2 diabetes, mortality increased in patients who had breast cancer (1.32 [1.17-1.49]) and prostate cancer (1.19 [1.08-1.31]).  It was decreased in patients with lung cancer (0.84 [0.77-0.92]).

The analysis by diabetes treatment regimen revealed that mortality was increased (relative to people without diabetes) in people on monotherapy with sulfonylureas (1.13 [1.05-1.21].  It was also increased in people on monotherapy with insulin (1.13 [1.01-1.27]).

However, mortality was decreased in people with type 2 diabetes on monotherapy with metformin (0.85 [0.78-0.93]).

It was confirmed in this study that having type 2 diabetes leads to poor prognosis after incident cancer.  However, that association can vary based on the type of diabetes treatment regimen and where the cancer is located.  Metformin was seen to have a survival benefit; this was seen both in comparison to other diabetes monotherapies (sulfonylureas and insulin) and in comparison to patients without diabetes.

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