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Rich
Sometime back, you asked me if there was any discussion at the 2009 Breast Cancer Symposium about ongoing support for metformin. Dr. Herman Kattlove, former medical editor for the American Cancer Socity, wrote in his private blog that he read an recent article touting the benefits of metformin (glucophage) in preventing cancer.
From what he gleamed in the article, almost all the evidence for cancer prevention by metformin comes from studies of people with diabetes. Diabetics are known to have higher rates of certain cancers - liver, pancreas, endometrium, colon/rectum, breast and bladder.
The issues for the speculation why this happens is the higher blood sugar in diabetics - sugar feeds cancer. The other issue is the higher amounts of insulin in their blood. People with type 2 diabetes have higher than normal amounts of insulin in their blood and the problem is they can't use it properly - they are relatively insensitive to insulin.
A large study of metformin and cancer was published in the November 2010 issue of the journal, Cancer Prevention Reserach. It was a meta-analysis which the authors reviewed and reported on all the well-documented studies of metformin and cancer in diabetics. They found that diabetic patients treated with metformin were about 25% less likely to develop or die from the typeical cancers found in diabetics.
The reason metformin reduces the cancer rate isn't known, however, scientists think it may be related to lower blood insulin levels or some interference with the cancer cells ability to use glucose. It is also known that metformin will slow cancer cell growth in test tubes and in mice.
The bigger issue Kattlove suggests is whether it will block cancer growth in non-diabetic people. Metformin is not an innocuous drug. It does interfere with metabolism - good for diabetics but who knows for non-diabetics?
NCI is sponsoring a study where metformin is being added to the usual drugs in patients with early stage breast cancer to prevent the cancer from coming back. Half the patients will get metformin and the rest will receive a placebo. It may take 5-10 years. In the meantime, he suggested forgetting about the drug. We just don't know if it will work and it may be harmful, unless you have adult-onset diabetes.
Greg
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