AACR. US: Among nonsmokers who had diabetes,
those who took the diabetes drug metformin had a decrease in lung cancer
risk, according to a study published in Cancer Prevention Research, a journal of the American Association for Cancer Research.
“Metformin
use was not associated with lung cancer risk when we looked at all
patients with diabetes. However, our results suggest that risk might
differ by smoking history, with metformin decreasing risk among
nonsmokers and increasing risk among current smokers,” said Lori C. Sakoda, PhD, MPH, research scientist at the Kaiser Permanente Division of Research in Oakland, California.
“Our
results suggesting that the risk associated with metformin might differ
by smoking history were unexpected,” added Sakoda. “Additional large,
well-conducted studies are needed to clarify whether metformin may be
used to prevent lung or other cancers, particularly in specific
subpopulations, such as nonsmokers.”
Some laboratory studies and a
number of observational studies suggest that metformin may prevent
cancer, but the data from human studies are conflicting, explained
Sakoda. The researchers conducted this study to further clarify the
association between metformin use and lung cancer risk.
Sakoda and
colleagues conducted a retrospective cohort study of 47,351 diabetic
patients (54 percent men), 40 years or older, who completed a
health-related survey between 1994 and 1996. Information on their
diabetes medications was collected from electronic pharmacy records.
About 46 percent of them were “ever-users” of metformin, defined as
those who filled two or more prescriptions within a six-month period.
During
15 years of follow-up, 747 patients were diagnosed with lung cancer. Of
them, 80 were never smokers, and 203 were current smokers.
Metformin
use was not associated with lower lung cancer risk overall; however,
the risk was 43 percent lower among diabetic patients who had never
smoked, and the risk appeared to decrease with longer use. Nonsmokers
who used metformin for five years or longer had a 52 percent reduction
in lung cancer risk, but this finding was not statistically significant.
Metformin
use for five or more years was associated with a 31 percent decrease in
the risk for adenocarcinoma, the most common type of lung cancer
diagnosed in nonsmokers, and an 82 percent increase in the risk for
small-cell carcinoma, a type of lung cancer often diagnosed in smokers,
but neither of these findings were statistically significant.
This
study was funded by the National Institutes of Health. Sakoda declares
no conflicts of interest. Assiamira Ferrara, Charles Quesenberry Jr.,
and Laurel Habel, coauthors on this study, have received research
funding from Takeda to Kaiser Foundation Research Institute for a study
of pioglitazone and cancer and from Sanofi through a subcontract from
University of North Carolina to Kaiser Foundation Research Institute for
a study of insulin glargine and cancer. Habel has received additional
research funding from Genentech to Kaiser Foundation Research Institute
for a study of HER2-positive breast cancer, including risk of
cardiotoxicity following trastuzumab.