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The oral sugar-lowering drug metformin has been in the cancer news quite a bit as of late. This drug, which is now off patent, is very cheap and safe--used by millions of people with diabetes worldwide. In the last few years, it has been associated with lower rates of breast and pancreatic cancers. A large database study of patients in the UK showed that patients on long-term metformin had about half the risk of developing breast cancer compared to non-users, including those with diabetes who took insulin or another class of oral sugar-lowering drugs called sulfonylureas. And in breast cancer patients, it seems to be associated with greater responses to chemotherapy. This past week, at the American Association for Cancer Research meeting, researchers at the National Cancer Institute showed it can lower lung cancer rates in animals exposed to nicotine-like carcinogens. Metformin inhibits insulin and insulin-like growth factors, both of which produce growth signals that can lead to cell growth. In contrast, insulin and other diabetes drugs can stimulate these pathways--in fact, insulin use has been implicated in slightly higher risks of breast cancer.This is one of several examples of the anti-cancer potential of several older drugs used for other diseases. So far the story with metformin is very appealing in that it has a long and safe track record. Based on this background, The National Cancer Institute of Canada is planning a large early-stage breast cancer trial of standard therapy with or without metformin for five years. It will be interesting to see if an old drug that has no patent life can actually be developed for use in cancer.