MONDAY, Jan. 24 (HealthDay News) -- Heavy smokers of
childbearing age -- especially women who have not been pregnant --
may face a modest increase in their risk of developing breast
cancer, a new study suggests.
Researchers from Brigham and Women's Hospital and Harvard
Medical School in Boston found that breast cancer among
pre-menopausal women was associated with greater cigarette amounts
over a longer time period, including taking up the habit at a
Using data collected from the Nurses' Health Study, initiated in
1976 with funding from the U.S. National Institutes of Health, the
scientists examined medical records of 111,140 women over 30 years
for active smoking and 36,017 women over 24 years for secondhand
About 8,700 of those women went on to develop breast cancer, the
most common cancer affecting women worldwide. Pre-menopausal heavy
smokers had a 6 percent higher incidence of malignancy, according
to senior study author Karin Michels.
However, secondhand smoke exposure in childhood or adulthood
didn't appear to elevate breast cancer risk, although the authors
noted that such exposure is hard to assess. Light and moderate
smoking did not seem to raise breast cancer risk either, the
"I think we confirmed the fact that smoking is not an important risk for breast cancer," Michels said. "Obviously, smoking is a very important carcinogen, and most cancers are affected by smoking. Breast cancer is probably less affected."
Those most at risk of developing breast cancer began smoking
before age 18, smoked 25 or more cigarettes a day or smoked more
than 35 years, according to the study, reported in the Jan. 24
issue of the
Archives of Internal Medicine.
Michels, a cancer epidemiologist and associate professor of
obstetrics and gynecology at Brigham and Women's Hospital, said the
study's large size made it easier to clarify conflicting results
from previous research.
Estrogen can fuel cancer growth, and researchers believe that
smoking has anti-estrogenic effect in women, lowering the amount or
activity of the hormone. Consistent with that belief is the study's
finding that smoking after menopause -- when hormone levels dip
dramatically -- may be associated with a slightly decreased risk of
"Postmenopausal women in particular have an increased risk of cardiovascular disease," Michels said. "If she adds smoking on top of that, I think it's bad. This is definitely not a license to smoke."
Dr. Mary B. Daly, director of cancer prevention and control at
Fox Chase Cancer Center in Philadelphia, praised the study for
using a longstanding, large number of participants.
"The study is done very carefully," Daly said. "It's an interesting field because, as the authors point out, the data so far have been conflicting."
Women's breasts are more sensitive to carcinogens before
experiencing a full-term pregnancy, Daly noted, making smoking
potentially more dangerous for them than for pre-menopausal women
who have given birth.
"The good thing about this study is that it's not going to change anything we're going to say to people about smoking," Daly said. "In terms of public health recommendations, you still want to give the message that smoking is not healthy."
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