Several previous studies have reported that diabetes is associated with shortened survival among breast cancer patients. Survival is also reduced by elements of metabolic syndrome, including obesity, insulin resistance and high cholesterol. There is some evidence that Lantus (insulin glargine), a long-acting insulin used by some diabetics, could promote breast cancer. On the other hand, metformin, which is widely used to treat type 2 diabetes, appears to reduce risk of breast cancer and its recurrence. Now a new Taiwanese study has reported that diabetes reduces survival among early stage breast cancer patients.

The study was designed to investigate the impact of diabetes on survival after a diagnosis of breast cancer. To conduct the study, the authors used data in the Taiwan Cancer Registry regarding women diagnosed with early-stage breast cancer between 2003 and 2004. Diabetes status and data concerning other health problems (comorbidities) of the women were retrieved from Taiwan's National Health Insurance database.

The study included a total of 4,390 breast cancer patients, of whom 341 (7.7%) had diabetes. This is a lower proportion than that found in U.S. breast cancer patients. Death rates were found to be significantly higher among breast cancer patients with diabetes, both death from breast cancer and death from other causes. Among those with diabetes, the five-year breast cancer-specific survival rate was 85% compared to 91% among those without diabetes. Similarly, five-year overall survival was significantly lower in diabetic patients (79%) than in non-patients (90%). The findings held when adjusted for other health problems and breast cancer-related variables. The authors conclude that diabetes is an independent predictor of lower survival rates in this population, even after adjusting for concurrent illnesses.

Please see our article on diabetes and breast cancer for more information.