M. T. Redaniel of University of Bristol in Bristol, UK and colleagues conducted the case-control study and found women with breast cancer who also suffered type 2 diabetes mellitus were 40 percent more likely to die from all causes, compared with those with breast cancer only.
The association, which was derived already after adjustment for age, period, region, smoking status, body mass index, alcohol drinking and deprivation, was based on data from 52,657 women with type 2 diabetes diagnosed between 1987 and 2007 and 30,210 randomly selected women without type 2 diabetes.
This association can be easily understood. Type 2 diabetes mellitus patients have insulin insensitivity or insulin resistance and tend to produce more insulin than people without diabetes type 2 do. When insulin is produced, insulin-like growth factor-1 is also produced, which is known to promote cancer growth.
Type 2 diabetes mellitus was also associated with 29 percent increased overall risk for developing breast cancer. This association was attenuated after adjustment for other factors like age, period of cohort entry, region, and BMI. That is, women with type 2 diabetes were 12 percent more likely than those without the disease to develop breast cancer.
Diabetes treatments may make some difference in the risk of developing breast cancer. Compared with sulfonylurea, metformin monotherapy and insulin therapy were associated with 4 and 33 percent increased risk of developing breast cancer among women with diabetes. From the study report abstract, it is unknown whether using sulfonylurea would increase risk of breast cancer.
Of all the associations, the one between being diabetic and risk of breast cancer was the strongest, suggesting that it is important to maintaining adequate glycemic control alongside cancer treatment, the researchers concluded.
The findings suggest that type 2 diabetes may increase risk of developing breast cancer and death from the disease.
By David Liu, PHD