Older women who smoke cigarettes or have smoked for long periods of time may be up to 40 percent more likely to develop breast cancer than women who never smoked, according to a new study.
The results also suggest that use of combination estrogen plus progestin hormone therapy among older women who smoke could as much as double their risk of developing cancer.
Researchers say the results add to growing evidence that breast cancer may be yet another health risk associated with cigarette smoking.
"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," says researcher Christopher I. Li, MD, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, in a news release. "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."
Smoking May Raise Breast Cancer Risk
Researchers say the study is the first study to look at the link between smoking and breast cancer in nearly 2,000 postmenopausal women between the ages of 65 and 79.
Women of this age range may have smoked for very long durations, they write. Risk factors relating to breast cancer vary with age. Because a woman’s breast cancer risk increases with age, the causes of breast cancer in older women may be different from younger women, they add.
“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," says Li.
The results showed a 30 to 40 percent increased risk of breast cancer among:
--Women who were current or long-term smokers (a pack a day for 11 years or more)
--Women who started smoking at a younger age
--Women who started smoking before the birth of their first child
The study also showed that women who had smoked cigarettes for 20 years or more and used combination hormone replacement therapy were more than twice as likely to develop breast cancer as women who have never smoked or used hormone replacement therapy.
"We are really not sure what that finding means because this correlation hasn't been reported in prior studies," says Li. "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."
Never Too Late to Quit Smoking
Because the study involved older women, researchers say they were also able to look at the impact of quitting smoking on long-term breast cancer risk.
The results showed that the risk of breast cancer decreased as the number of years since the women quit smoking increased.
For example, researchers say that within about 10 years after a woman stops smoking her risk of breast cancer falls back to the level of a woman who has never smoked.
SOURCES: Li, C. Cancer Causes and Control, October 2005; vol 16: pp 975-985. News release, Fred Hutchinson Cancer Research Center.