STOCKHOLM – Excitement is rising in the diabetes and oncology worlds regarding the potential anticancer effects of metformin.
“An off-patent, old drug, famous for its role in type 2 diabetes, is now a hot topic in cancer research,” Dr. Michael Pollak said at a press briefing at the meeting.
Epidemiologic data have shown that rates of colon, lung, breast, and prostate cancer among diabetes patients treated with metformin are lower than those of the general population (BMJ 2005;330:1304-5 and Diabetes Care 2010;33:1304-8).
“We don't mean 2% lower or 10% lower: It was roughly half the expected cancer rate. Cancer epidemiologists pay a lot of attention when we see that kind of a finding to try and prove that it's an artifact or some kind of mistake, because a reduction of cancer mortality of 50% is something we've never seen before as a consequence of any prevention strategy,” said Dr. Pollak, professor of medicine and oncology at McGill University, Montreal.
Since all the epidemiologic data are retrospective, researchers initially were skeptical. But laboratory studies supported the epidemiology, showing that metformin appears to reduce tumor aggressiveness in a variety of cancer models (Cancer Res. 2007;67:10804-12 and 2006;66:10269-73).
There are several theories about the mechanism. Metformin acts primarily in the liver, where it reduces glucose secretion. The drug also reduces insulin levels, which could inhibit tumors whose growth is stimulated by insulin.
Research is aimed at determining precisely which molecular subtypes are likely to respond. “We don't believe it will work uniformly in all tumors in all people,” said Dr. Pollak, who is also director of the Cancer Prevention Centre at SMBD–Jewish General Hospital, Montreal.
Research is “administratively unusual,” because the drug is off patent, so there is limited private sector interest. But academic research is taking off in many countries, with many proposed and some initiated epidemiologic studies, laboratory investigations, and even clinical trials of nondiabetic patients with cancer.
“We're not here to announce the final conclusions. We're here to share the excitement that something unexpected and interesting has happened, and it's now under investigation,” Dr. Pollak said.
It's too early to suggest that cancer patients begin taking metformin. Even so, “If you have cancer and diabetes that can be controlled by metformin, metformin becomes a pretty rational choice at this point. Not because we're sure it will help, but because there's a chance.”
Dr. Pollak has ties to or has consulted for Novo-Nordisk, Eli Lilly & Co., Pfizer Inc., Sanofi-Aventis, and Boehringer Ingelheim GmbH.