What Does The Current Evidence Show
There are some things that research has told us about smoking and breast cancer. Lets examine what we know.
It appears that breast cancer risk is linked to a smoking habit thats lasted for many years. For example, people with a history of smoking have about a breast cancer risk than people whove never smoked.
A found that the risk of breast cancer increased in women who:
- currently smoke or previously smoked a large number of cigarettes
- started smoking at a younger age
- smoked for many years
- smoke a higher number of pack-years, with risk increasing with every 20 pack-years
- smoked before the birth of their first child
A more recent looked at data pooled from 14 different cohort studies and found that:
- The overall association of smoking with breast cancer was modest.
- Smoking for more than 10 years before the birth of a first child carried a high risk of breast cancer.
- Smoking 40 or more cigarettes per day was associated with the highest risk of breast cancer.
- Drinking alcohol can have a compounding effect on breast cancer risk, particularly when heavy drinking is combined with smoking a large number of cigarettes or smoking for many years.
Exposure to secondhand smoke may also increase a womans risk of breast cancer. A found that women who were frequently around secondhand smoke had similar breast cancer risk to active smokers.
Studies In Specific Subgroups
The association between cigarette smoking and breast cancer risk has sometimes been more or less evident in certain subgroups of the studied populations, subgroups defined by factors such as menopausal status, age , whether or when a woman had children, or certain genotypes. Such effect modification might reflect differences in the biological parameters underlying the association or methodological factors such as differences that occur by chance or with the varying prevalence of confounding variables. It is also possible that effect modification reflects differences in the opportunities for exposure to cigarette smoke, such as those that might occur if postmenopausal women were more likely than premenopausal women to have been exposed to cigarette smoke for 40 years or more. Nonetheless, studies that stratify results according to certain factors of interest may help to clarify the association between cigarette smoking and breast cancer risk and may ultimately help to reconcile the disparate findings noted earlier.
Menopausal Status.
Studies of cigarette smoking and breast cancer risk according to menopausal status
Smoking in Very Young Women.
Smoking before or after a First Full-term Pregnancy.
Studies of cigarette smoking before, during, and after a first full-term pregnancy, and breast cancer risk
NAT and Other Genotypes.
Table
Studies of cigarette smoking and breast cancer risk according to NAT2 genotypes
ER and PR Status.
Study Design And Participants
The Norwegian Women and Cancer Study cohort profile has been previously described in detail., Briefly, the Central Population Register selected a random sample of women according to year of birth. Subsequently, an invitation to participate in the study, with a baseline questionnaire and a pre-stamped return envelope enclosed, was mailed to each woman. The National Data Inspectorate and the Regional Committee for Medical and Health Research Ethics approved the study. All women gave informed consent.
Women who completed a questionnaire during three waves of data collection, namely 19911992, 19961997 and 20032007 , were the baseline population. The overall response rate was 52.7%. We excluded women with prevalent cancer , who had emigrated , who died before start of follow-up , who were born after 1957 , who had missing information or were ever-smokers or had missing information on exposure to SHS from parents during childhood . Altogether, 8542 women with breast cancer were excluded in this process. The analytical cohort comprised the 45 923 remaining women.
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Is There A Direct Link
A 2014 report from the Surgeon General evaluated available studies on the potential health consequences of smoking. It found sufficient evidence of potential ways in which smoking may cause breast cancer.
However, the report concluded that while the evidence is suggestive, its not enough to say that smoking or exposure to secondhand smoke causes breast cancer. More research is needed to establish a direct link between smoking and breast cancer.
Who Is Most Vulnerable To The Health Effects
Overall, research suggests earlier exposures to tobacco smoke are of greater concern.
- Some studies indicate smoking before a first full-term pregnancy may increase the risk of a later diagnosis of breast cancer.,
- Smoking during adolescence has been found to be associated with increased breast cancer risk.,,,,
- Studies also suggest increased risk of breast cancer for pre-menopausal women.
- Individuals who have smoked for a long time or have smoked heavily seemed to have higher risks for breast cancer.
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Is Abortion Linked To Breast Cancer Risk
A few retrospective studies reported in the mid-1990s suggested that induced abortion was associated with an increased risk of breast cancer. However, these studies had important design limitations that could have affected the results. A key limitation was their reliance on self-reporting of medical history information by the study participants, which can introduce bias. Prospective studies, which are more rigorous in design and unaffected by such bias, have consistently shown no association between induced abortion and breast cancer risk . Moreover, in 2009, the Committee on Gynecologic Practice of the American College of Obstetricians and Gynecologists concluded that more rigorous recent studies demonstrate no causal relationship between induced abortion and a subsequent increase in breast cancer risk . Major findings from these studies include:
- Women who have had an induced abortion have the same risk of breast cancer as other women.
- Women who have had a spontaneous abortion have the same risk of breast cancer as other women.
- Cancers other than breast cancer also appear to be unrelated to a history of induced or spontaneous abortion.
Strengths And Limitations Of The Study
Our studys strengths include the prospective design, the large size and broad geographical distribution of the cohort, the large number of cancer cases, pathological confirmation of cases by trained adjudicators and cancer coders, detailed information on potential confounders, and, particularly, detailed information on passive smoking, including quantitative measures of exposure in childhood and adult exposure in residential and workplace settings.
However, our study also has limitations. One is that we used only baseline values for womens smoking status and all covariates and did not account for changes in exposure during follow-up, which may have caused some exposure misclassification and biased our results towards the null. However, given that our study population consisted of postmenopausal women and that few were current smokers, the effect of changes in smoking status during follow-up is likely to have been minimal. Based on yearly reassessment of smoking status in the Womens Health Initiative, about 60% of smokers continued to smoke for six years of follow-up and 99% of non-smokers remained abstinent.
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Does Smoking Increase My Risk For Breast Cancer
Dr. Sellers answers the question: ‘Does Smoking Increase Breast Cancer Risk?’
— Question: Does smoking increase my risk for breast cancer?
Answer: I’d like to start by pointing out that if we eliminate smoking we would reduce all cancer-related mortality by 30 percent. best we know that cigarettes, in any form, are not safe. In relation to breast cancer, in particular, most of the studies haven’t found a striking increase, but some of that may be because of the smoking habits of women. Smoking was uncommon in this country prior to World War II. And when women started smoking they tended to be adults when they started the habit.
Ninety-five percent of smokers in this country start as teenagers and that might be a particularly susceptible time for women — when their breasts are growing and maturing and tissues rapidly dividing. That, I think, is a question that we’re going to need to pay close attention to and continue to study. So, currently, there isn’t evidence that it increases risk. There’s certainly no good reason why one should continue to smoke or feel like they’re safe if they do smoke.
Smoking And Drinking By The Numbers
- 20 percent of American adults, nearly 38 million people, are smokers.
- 70 percent of American smokers, more than 26 million people, also drink.
- 80 to 95 percent of alcoholics are smokers.
- 70 percent of alcoholics are heavy smokers .
- 80 percent of throat and mouth cancer in men and 65 percent of throat and mouth cancer in women are linked to the combination of smoking and drinking.
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Epidemiological Studies Of Cigarette Smoking And Benign Breast Disease
Studies of an exposure such as cigarette smoking and the risk of a condition known to be a precursor to a disease, especially a disease that develops after a considerable latency period, may provide insight into the association between the exposure and the disease itself. For example, smoking has been associated consistently with precursors of colorectal cancer, namely, colorectal adenomas, even though its association with colorectal cancer itself has not been consistent . Because most colorectal cancers develop from adenomas , either the positive association with adenomas stems from bias, such as that which would occur if smokers were more likely to undergo endoscopy, or smoking acts early in the cancer process, but not later. Under the latter circumstance, the association with cancer may not be detected because a study is conducted before sufficient time has elapsed between smoking initiation and cancer development indeed, investigators have recently hypothesized that a very long induction period separates colorectal cancer initiation due to smoking and its clinical manifestations, and it is only in studies conducted recently that a consistent association between cigarette smoking and colorectal cancer risk has become evident .
Table
Studies of cigarette smoking and benign breast disease
Who Is Most At Risk Of Developing Breast Cancer
1. The strongest risk factor for breast cancer is age. Therefore, older women are at a higher risk of developing breast cancer than younger women.
2. Another significant risk factor is carrying a gene that predisposes to the development of breast cancer, such as the BRCA 1 and 2 genes. Related to carrying a gene that causes breast cancer, having a strong family history of breast cancer also increases a persons risk. Women who carry a gene that causes breast cancer or women who have a strong family history of breast cancer are at higher risk than women who do not.
3. Another risk factor for breast cancer is having a history of a breast biopsy that showed atypical cells, such as atypical ductal hyperplasia or lobular carcinoma in situ.
4. Lastly, there are several risk factors associated with a woman’s exposure to hormones throughout her lifetime, such as early menarche, number of pregnancies, whether or not a woman has breastfed, late menopause, that impact breast cancer risk. The more a woman has been exposed to estrogen and the more menstrual cycles she has experienced, the higher her risk of developing breast cancer.
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Reproductive History Estrogen Is The Main Hormone Associated With Breast Cancer Estrogen Affects The Growth Of Breast Cells Experts Believe That It Plays An Important Role In The Growth Of Breast Cancer Cells As Well The Type Of Exposure And How Long Cells Are Exposed To Estrogen Affects The Chances That Breast Cancer Will Develop
Early menarche
The start of menstruation is called menarche. Early menarche is when menstruation starts at an early age . Starting your period early means that your cells are exposed to estrogen and other hormones for a greater amount of time. This increases the risk of breast cancer.
Late menopause
Menopause occurs as the ovaries stop making hormones and the level of hormones in the body drops. This causes a woman to stop menstruating. If you enter menopause at a later age , it means that your cells are exposed to estrogen and other hormones for a greater amount of time. This increases the risk for breast cancer. Likewise, menopause at a younger age decreases the length of time breast tissue is exposed to estrogen and other hormones. Early menopause is linked with a lower risk of breast cancer.
Late pregnancy or no pregnancies
Pregnancy interrupts the exposure of breast cells to circulating estrogen. It also lowers the total number of menstrual cycles a woman has in her lifetime.
Women who have their first full-term pregnancy after the age of 30 have a slightly higher risk of breast cancer than women who have at least one full-term pregnancy at an earlier age. Becoming pregnant at an early age reduces breast cancer risk.
The more children a woman has, the greater the protection against breast cancer. Not becoming pregnant at all increases the risk for breast cancer.
Smoking Before First Childbirth
Young age at first birth and increasing parity confer long-term protection against breast cancer , and animal models point to terminal differentiation of breast tissue at full-term pregnancy being important in this process . Increased risks have been reported for invasive breast cancer if smoking started before first childbirth , but we found the association was significant only if we did not adjust for age at first pregnancy. Researchers in a number of previous studies have adjusted for age at first pregnancy and still found significant associations with interval to first birth however, it is difficult to determine the adequacy of adjustment. For example, in a large pooled analysis of 14 cohort studies, there was a strong trend with smoking interval before first birth after adjustment for potential confounders that included age at first birth and number of live births , whereas after stratification by age at first birth, the trends in each stratum were weaker , which is suggestive of confounding.
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Association Of Active And Passive Smoking With Risk Of Breast Cancer Among Postmenopausal Women: A Prospective Cohort Study
- Accepted 11 January 2011
A Note On The Analysis Of Cigarette Smoking
Qualitative measures of smoking have been used in most previous studies of breast cancer risk. Quantitative measures of smoking frequency , duration , the product of smoking frequency and duration , latency , and recency have been used more frequently in recent years, although use of these measures remains sporadic, and rarely have most or all of these measures been examined in the same study. The fact that the various smoking measures are correlated with each other complicates the differentiation of their independent effects. For example, smokers of high intensity tend to be smokers of long duration, and the latter tend also to have commenced smoking at an early age. In such instances, to examine their independent effects, one can attempt to mutually adjust for various smoking measures in multivariate models or examine a particular smoking measure over strata of another. Pack-years, a potentially useful combined measure of smoking intensity and duration, has conceptual limitations, because 20 pack-years can accrue by smoking two packets of cigarettes per day for 10 years, for example, or by smoking a half of a packet of cigarettes per day for 40 years.
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Using An Intrauterine Device
Women who used an intrauterine device for birth control seem to have a lower risk of getting endometrial cancer. Information about this protective effect is limited to IUDs that do not contain hormones. Researchers have not yet studied whether newer types of IUDs that release progesterone have any effect on endometrial cancer risk. But these IUDs are sometimes used to treat pre-cancers and early endometrial cancers in women who wish to be able to get pregnant in the future.
Measurement Of Exposures And Confounders
All information on exposures and confounders used in this analysis was collected at baseline. Information on active smoking included smoking status , and women who were current or former smokers were also asked the age at which they started smoking, the number of cigarettes smoked per day, and the duration of smoking in years. Among former smokers, age at quitting smoking was also collected. Pack years of smoking were calculated by multiplying the total years of smoking by the number of cigarettes smoked a day divided by 20.
Questions on exposure to passive smoking related to each of the following: childhood , adult home, adult work, current home, and current work . Women who reported any of these exposures were also asked the number of years of exposure in childhood, as an adult at home, and as an adult at work .
The potential confounders used in multivariable analyses included age at enrolment , ethnicity , education , body mass index , physical activity , alcohol intake , parity , family history of breast cancer , history of hormone therapy use , age at menarche , and age of first live birth .
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