Researchers found that women between 20 and 44 years
old who had smoked a pack of cigarettes per day for at least 10
years were 60 percent more likely than those who smoked less to
develop so-called estrogen receptor-positive breast cancer.
Smokers were not more likely to develop a less common form of breast
cancer known as triple-negative breast cancer, which tends to be
"I think that there is growing evidence that breast cancer is
another health hazard associated with smoking," Dr. Christopher Li
told Reuters Health.
Li is the study's senior author from the Fred Hutchinson Cancer
Research Center in Seattle.
Previous research has found links between smoking and breast cancer,
Li and his colleagues note in the journal Cancer. The studies
looking at breast cancer among younger women have produced
conflicting results, however.
They also say there are still questions about whether smoking is
linked to an increased risk of some types of breast cancer but not
"I think there is a growing appreciation that breast cancer is not
just one disease and there are many different subtypes," Li said.
"In this study, we were able to look at the different molecular
subtypes and how smoking affects them."
He and his team analyzed data from young women in the Greater
Seattle area who were diagnosed with breast cancer between 2004 and
Of those women, 778 were diagnosed with the more common estrogen
receptor-positive type and 182 had the less common but more
aggressive triple-negative type.
The researchers also included information from 938 cancer-free women
According to the National Cancer Institute, about one in every eight
American women will eventually develop breast cancer — but the risk
is lower at younger ages. Only about one in every 227 30-year-old
women — or less than half a percent of them — will develop breast
cancer before the age of 40, for example.
In this study, young women who had ever smoked were about 30 percent
more likely to develop any type of breast cancer, compared to women
who had never smoked.
When the researchers looked at each type of breast cancer
separately, there was no link between smoking and triple-negative
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But women who were recent or current smokers and had smoked for
at least 15 years were about 50 percent more likely to have estrogen
receptor-positive breast cancer, compared to women who had smoked
for fewer years.
And those women who reported smoking at least one pack a day for 10
years were 60 percent more likely to have that type of cancer,
compared to lighter smokers.
It could be that some of the substances found in cigarettes act like
estrogens, which would promote estrogen receptor-positive breast
cancer, the researchers write.
"There are so many different chemicals in cigarette smoke that
can have so many kinds of effects," Li said.
Geoffrey Kabat cautioned that some of the effects found in the new
study are small and not clear-cut.
Kabat was not involved with the study, but has researched the
effects of smoking on breast cancer risk. He is also an
epidemiologist at the Albert Einstein College of Medicine of Yeshiva
University in Bronx, New York.
He told Reuters Health the findings of previous studies are not
"We know smoking is bad for you and the earlier you smoke and the
more often you smoke the worse off you're going to be in terms of
many outcomes, but the role of smoking in breast cancer is not
clear," Kabat said. "There may be something going on and it may be a
modest effect in some subgroups."
Cancer, online Feb. 10, 2014.
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