More hints, still no proof metformin fights cancer Wednesday, June 13, 2012 By
Frederik Joelving NEW YORK (Reuters Health) - A new study is
fueling hopes that metformin, a cheap and relatively safe diabetes drug, might
have cancer-fighting properties. Researchers
found that women with diabetes who took the medication had a 25-percent lower
risk of developing breast cancer over more than a decade of follow-up. But like all previous studies of metformin's
suspected anti-cancer effects, the new findings fall short of proving the
compound can stave off the big C. "This
is an area of great excitement," said Dr. Pamela Goodwin, who wrote an
editorial about the study, published in the Journal of Clinical Oncology. "The evidence is coming together that
metformin may actually have a clinically relevant effect, but none of this is
good enough to change clinical practice just yet," added Goodwin, a breast
cancer expert at Mount Sinai Hospital in Toronto ,
Canada . Metformin (also sold under the brand name
Glucophage) has been on the market for many years and is generally considered
safe, although five to 10 percent of patients experience side effects like
nausea and bloating. Because its original patent has expired, a month's worth
of pills can be bought for less than $10.
It is used by millions of type 2 diabetics every day to help control
their blood sugar. Intriguingly, metformin also shrinks lung and breast tumors
in mice, and several reports show people taking it for diabetes appear to
develop cancer less often. That's why
scientists are hopeful it might someday be used to prevent cancer in smokers
and others at high risk of the disease. The
new study used data from about 68,000 postmenopausal women who took part in the
U.S.
government-funded Women's Health Initiative clinical trials. Over nearly 12 years of observation, there
were more than 3,200 new cases of breast cancer among the women. Every year, 0.42 percent of women without
diabetes developed breast cancer, compared to 0.40 percent of diabetics on
metformin and 0.47 percent of diabetics taking other drugs. After taking into account risk factors for
breast cancer, the gap between women without diabetes and diabetics on drugs
other than metformin vanished. But diabetics on metformin turned out to have a
25-percent lower cancer risk than their diabetes-free peers. Goodwin said the new study is the best of its
kind so far, but nonetheless relies on observations instead of an actual
experiment in which women are randomly selected to take metformin or not. "All of these observational studies,
what they do is they generate hypotheses," she told Reuters Health.
"I think we need to be cautious about taking these observations and
applying them to people without diabetes."
Dr. Rowan Chlebowski, who led the study, said his results don't necessarily
mean diabetics should switch to metformin if they are not already taking it. "The significance is identifying
potential other uses for drugs we have great safety information on, as opposed
to new drugs," Chlebowski, of the Los Angeles Biomedical Research
Institute at Harbor-UCLA Medical Center in Torrance, told Reuters Health. "You
should have whatever treatment is best for your diabetes," she said.
"Most diabetics are already on metformin, but the key is they should get
good blood sugar control." Goodwin
and her colleagues are currently running a $25 million trial to test whether
metformin can help ward off new tumors in women getting breast cancer
treatment. The results are expected in three to four years. Goodwin said nobody has yet begun a study to
see if the drug can prevent healthy people from getting cancer in the first
place. "At a societal level, we
have to develop mechanisms to take the inexpensive generic drugs that seem to
have anti-cancer effects and study them," she added. According to the American Cancer Society, one
in eight women will develop breast cancer at some point, although less than
three percent of all women will die of the disease. SOURCE: http://bit.ly/L86p7l Journal of Clinical Oncology, online June
11, 2012. Reuters Health
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