Combination HRT Appears to More Than Double the Risk in Women Who Smoke
SEATTLE, Sept. 27 /PRNewswire/ -- Older women who have smoked for 11 or
more "pack years" -- the lifetime equivalent of a pack a day for at least 11
years -- face a 30 percent to 40 percent increased risk of developing breast
cancer as compared to women who've never smoked, according to new findings
from researchers at Fred Hutchinson Cancer Research Center.
What's more, the researchers found that long-term smokers who add
combination hormone-replacement therapy (estrogen plus progestin) to the mix
increase their odds of getting breast cancer by 110 percent: more than double
that of women who've never smoked or taken HRT.
These findings, by Christopher I. Li, M.D., Ph.D., and colleagues, appear
online and will be published in the October print edition of Cancer Causes and
Control.
While a number of studies have looked at the association between smoking
and breast cancer, many have been inconclusive and many have had conflicting
results, Li said, largely because of limitations in data collection, such as
not taking into account the duration or intensity of smoking or the timing of
smoking onset. In addition, few previous studies have focused on older,
postmenopausal women who've had a particularly long smoking history.
"Ours is one of the only population-based studies of its kind to focus on
the association between smoking and breast-cancer risk in older women between
the ages of 65 and 79. Those who did smoke had much longer histories of
smoking than women in previous studies, so we were able to look at the effects
of long smoking durations on breast-cancer risk," said Li, an assistant member
of the Hutchinson Center's Public Health Sciences Division.
This study is the first of its kind to examine a wide variety of smoking
parameters, such as how long and how often a woman has smoked, the number of
pack years smoked, whether she was a former or recent smoker, her age at
smoking onset, and whether she started smoking before her first full-term
pregnancy.
"We found a 30 to 40 percent increased risk of breast cancer among women
who were current or long-term smokers, women who started smoking at a younger
age and also women who started smoking before their first full-term birth," Li
said.
The timing of smoking onset, particularly in relation to first pregnancy,
may be related to breast-cancer risk because of the known protective effect of
pregnancy on breast tissue. "During pregnancy, breast cells undergo a process
called differentiation, which makes them less susceptible to carcinogens,
whereas breast cells in women who have never given birth are less
differentiated and therefore may be more vulnerable to carcinogenic insults
from the toxins in cigarettes," Li said.
The population-based case-control study, funded by the National Cancer
Institute, involved nearly 2,000 older women in the Seattle-Puget Sound
metropolitan area. Half of the women had a history of breast cancer and half
served as a healthy control, or comparison, group. Study participants were
interviewed in person and were asked about a variety of factors known to
influence breast-cancer risk, including hormone and alcohol use, and
reproductive and family history. Even after statistically controlling for
these factors, smoking emerged as a significant, independent risk factor for
breast cancer, Li said.
Perhaps the most surprising finding surrounded the observation that
combined hormone therapy appears to significantly increase breast-cancer risk
in women who smoke long term (those with a history of 20 or more pack years of
smoking).
"We are really not sure what that finding means, because this correlation
hasn't been reported in prior studies," Li said. "We only saw the association
in smokers who used both estrogen and progestin and not among women who used
estrogen alone. We will follow up on this finding in future studies to see if
it can be replicated."
Another interesting -- and encouraging -- finding was that once a woman
stops smoking, within about 10 years of quitting her risk of breast cancer
falls back to that of a never-smoker. This suggests that recency of smoking
may be particularly important with respect to breast-cancer risk, Li said.
"We know that smoking is associated with a lot of diseases, from lung
cancer to heart disease, but the association with breast cancer is still
somewhat controversial," said Li, who is also an assistant professor of
epidemiology at the University of Washington School of Public Health and
Community Medicine. "Certainly, the association between smoking and breast
cancer is nowhere near as strong as the association between smoking and lung
cancer, but breast cancer may be another disease to add to the long list of
serious health issues related to smoking."
At Fred Hutchinson Cancer Research Center, our interdisciplinary teams of
world-renowned scientists and humanitarians work together to prevent, diagnose
and treat cancer, HIV/AIDS and other diseases. Our researchers, including
three Nobel laureates, bring a relentless pursuit and passion for health,
knowledge and hope to their work and to the world. For more information,
please visit fhcrc.org.
CONTACT
Kristen Woodward
206-667-5095
kwoodwar@fhcrc.org
SOURCE Fred Hutchinson Cancer Research Center
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Related links:
http://www.fhcrc.org
CONTACT:
Kristen Woodward of Fred Hutchinson Cancer
Research Center, +1-206-667-5095, or kwoodwar@fhcrc.org
NOTE TO EDITORS: To obtain a copy of the paper, "The Relationship
Between Various Measures of Cigarette Smoking and Risk of Breast
Cancer Among Older Women 65-79 Years of Age (United States),"
please contact Kristen Woodward in Hutchinson Center media
relations, 206-667-5095 or kwoodwar@fhcrc.org.
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