By Jimmy Downs

Tuesday Nov 20, 2012 (foodconsumer.org) -- A new study in Clinical Breast Cancer suggests that diabetes drug metformin may help reduce risk of breast cancer and increase odds of sruvival from the disease in postmenopausal women who do not have diabetes mellitus.

Patrizia Pasanisi, MD of Fondazione IRCCS Istituto Nazionale dei Tumori in Milan, Italy and colleagues conducted the study and found using metformin in a dose of 1500 mg per day signfiicantly reduced serum insulin amd testosterone levels in postmenopausal women with breast cancer, but no diabetes mellitus.

Serum levels of insulin and testosterone may have an effect on both breast cancer incidence and prognosis, said the authors.  In women with diabetes mellitus, metformin can not only reduce glucose (hyperglycemia) and insulin levels, but also lower risk of breast cancer.  And in women with polycystic ovary syndrome, metformin lowered insulin and testosterone levels.

Because high serum levels of insulin and testosterone are associated with elevated risk for breast cancer, it has been proposed that metformin may be used to prevent or treat breat cancer in women who do not have diabetes mellitus.

Enrolled in the study were 125 women who were diganosed with breast cancer, but no diabetes mellitus.  Testosterone levels were measured at 0.28 ng/mL (median value).  

Initially, breast cancer patients were asked to take 500 mg of metformin per day for three months and then 108 who completed the 3-month treatment were asked to continue to take 1000 mg/day for one month and then those who completed the one-month treatment were divided into two groups with one group receiving 1000 mg of metformin /day and another group receiving 1500 mg/day for five months.

As a result, women who took 1500 mg of metformin per day significantly lowered insulin, HOMA-IA index, testosterone and free androgen index levels, compared with those treated with 1000 mg per day.

At the end of the treatment with 1500 mg per day, the insulin level decreased by 25% and the testosterone level dropped 23%. 

The researchers concluded "Both these changes might have a prognostic importance" for postmenopausal women with breast cancer ,but no diabetes mellitus."