A common drug used to treat type 2 diabetes may soon join the arsenal of treatments for breast cancer. Metformin (brand names Glucophage, Glumetza, Fortamet, and Riomet) has several biochemical effects that are useful in controlling blood sugar. These effects may also control the growth of cancer cells. Dr. Ana M. Gonzalez-Angulo and Dr. Funda Meric-Bernstam of The University of Texas MD Anderson Cancer Center in Houston, Texas, provided a review of the potential for metformin treatment of breast cancer.
There are two lines of evidence for the benefits of metformin in treating cancer:
1. Retrospective studies of diabetes patients show that patients taking metformin have lower rates of cancer than patients who are not taking metformin.
2. Lab studies show that metformin inhibits the growth of cancer cells.
Gonzalez-Angulo and Meric-Bernstam explained that insulin and related biomolecules are important for cell growth both in healthy tissues and in cancer. Metformin alters cellular signaling pathways involved in the uncontrolled growth of cancer cells.
Metformin has a good safety record. Gonzalez-Angulo and Meric-Bernstam reported that cancer patients and their doctors should be concerned about the possibility of lactic acidosis, because the contrast chemicals used for imaging studies increase the risk for this condition. However, lactic acidosis is a rare side effect of metformin therapy in diabetics, occurring primarily in patients with kidney and/or liver disorders. More common side effects include nausea and diarrhea.
Dr. Ryan J. O. Dowling and colleagues at the Ontario Cancer Institute in Canada provided further details about metformin as a potential cancer treatment. Metformin is derived from the herb Galega officinalis, also known as French lilac, Goat's Rue, or Italian Fitch. The herb was used in ancient Egypt and medieval Europe to treat symptoms of diabetes. Metformin was approved for treatment of high blood sugar in Britain in 1958, in Canada in 1972, and in the United States in 1995.