Researchers have completed a study which shows that smoking can be a considerable factor causing the risk of breast cancer to be increased. The study also noted an, as yet unproven, link between exposure to second hand smoke and an increased incidence of breast cancer.
The study was published in the journal BMJ and was carried out by Juhua Luo, PhD, of West Virginia University, and colleagues and involved almost 80,000 participants, all women aged between 50 and 79. The original study ran from 1993 until1998 and was part of the Women’s Health Initiative Observational Study.
The findings reaffirms earlier research which has continued for more than 10 years that supports the belief of an association between smoking and an increased risk of breast cancer. Karen Margolis, MD, is a senior clinical investigator at HealthPartners Research Foundation in Minneapolis, and she says, “Since 2002, important studies with huge numbers of women have been showing a strong link. This adds to the weight of the evidence”.
Margolis says that all those involved with the study came from the United States and were a general cross section of the female population. Their backgrounds were all varied and throughout the ten year period that they were followed, 3,520 participants received a diagnosis of invasive breast cancer.
The study asked each woman to describe themselves as either a smoker, former smoker or someone who had never smoked. The non smokers had to answer questions about the amount of exposure to secondhand smoke they had experienced throughout their lives. The questions about smokers and former smokers related to smoking history, how many years they had smoked, how many cigarettes they smoked and if they were former smokers, how many years since they stopped smoking.
After analyzing all of the data the researchers found that smokers had a higher incidence of breast cancer diagnosis after the menopause when compared to non smokers. The likelihood of developing breast cancer being 16% more for smokers. The risk increased when the number of years a woman smoked was higher. And if women started smoking when they were young and before their first pregnancy then the risk of developing breast cancer rose up to 21%.
Stopping smoking had a clearly seen reduction on risk when compared to smokers but still remained 9% higher than those who never smoked in their lives. The researchers noted that although the risk drops when someone stops smoking, it can be as long as twenty years before the former smoker’s risk matches a lifetime non smoker.
Margolis believes that the conclusion is consistent and unambiguous when she says, “The link between smoking and breast cancer is ironclad.”
However, Paolo Boffetta, MD, deputy director of the Tisch Cancer Institute at Mount Sinai School of Medicine in New York City, thinks that further research is required. He does admit that the body of evidence is growing though, yet is cautious that the findings are still comparatively new. Boffetta is author of the editorial that came with the study conducted by Luo. He feels that, “It is a bit too early to say”. However, when talking of the future he says, “I’m a little bit cautious, but the evidence is becoming more and more convincing ... it will emerge more strongly in five or 10 years”.
Breast Cancer is more likely if you have been subjected to secondhand smoke
Part of the study was directed at investigating secondhand smoke and its effects on the risk of developing breast cancer. The researchers found that women, who reported the highest exposure to secondhand smoke, either at home or at their place of work, were 32% more likely to develop cancer than those with minimal exposure.
Because only 12% of the participants reported themselves as never having been exposed to secondhand smoke the comparison group was smaller. This led the researchers to say that further study is required to ensure that the finding is valid.
Margolis notes that, “Secondhand smoke was almost ubiquitous. Women aged 50-79 are almost universally exposed”.
Margolis accepts that the findings do not conclusively prove that secondhand smoke does cause breast cancer but she does say that,”it is biologically plausible that heavy secondhand smoke exposure could cause breast cancer”. She says the risk rises because, “You see the same type of damage to DNA in their breast cancer tissue in women who smoke and women exposed to secondhand smoke”.
Margolis also points out that the thought of breast cancer, as well as lung cancer and heart disease may be enough to help some women to stop smoking. She says that, “You can’t change your age, your genes, your family history, but you can add smoking to the list of risk factors”, and perhaps, “There are certain women for whom this message will be enough to convince them”.