Q: I was recently diagnosed with breast cancer and diabetes. The oncologist said that the metformin my primary care doctor put me on for diabetes will actually help kill the breast cancer cells. Can you explain how it does that? --- M.L., Roswell
A: There is growing evidence that metformin used to treat diabetes can slow the growth of cancer cells --- especially breast cancer.
The proposed mechanism by which metformin acts as an anti-breast cancer agent is that metformin lowers insulin levels. The hormone insulin stimulates cell growth, and cancer cells have six to 10 times the number of insulin receptors as do noncancerous cells.
Colon, breast, uterine, pancreatic and prostate cancer cells seem especially sensitive to the effects of insulin.
In particular, breast cancer cells are exquisitely sensitive to the effects of the insulin hormone. Insulin may also influence the activity of estrogen, another hormone that can trigger the growth of cancer cells.
It's been observed for some time that obese people have a higher incidence of colon, breast, uterine, pancreatic and prostate cancer. Obesity tends to be associated with higher levels of insulin and estrogen. It makes sense then that metformin used in the treatment of diabetes, insulin resistance and polycystic ovarian syndrome may be helpful as an adjunctive treatment for breast and other cancers.
Future research will be needed.
Will the use of insulin shots or diabetic drugs that increase insulin levels increase one's risk of breast and other cancers? The expert consensus at this point is that the benefit of properly treating diabetes and preventing its serious and irreversible complications outweighs the potential increased risk of developing cancer in the future.
Dr. Mitchell Hecht is a physician specializing in internal medicine. Send questions to him at: "Ask Dr. H," P.O. Box 767787, Roswell, GA30076. Because of the large volume of mail received, personal replies are not possible.
Copyright 2010 The Atlanta Journal-Constitution