Breast cancer risk factors: Difference between revisions

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==Risk Factors==
==Overview==
The primary risk factors that have been identified are: sex,<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref> age,<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCancer.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> childbearing, hormones,<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> high-fat diet,<ref>{{cite journal | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al. | title = Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS). | journal =J Natl Cancer Inst | volume =98 | issue =24 | pages =1767-1776 | pmid = 17179478 | url =}}</ref> alcohol intake,<ref name=Boffetta_2006>{{cite journal | last = Boffetta | first = Paolo | coauthors = Hashibe, Mia; La Vecchia, Carlo; Zatonski, Witold; Rehm, Jürgen | title = The burden of cancer attributable to alcohol drinking | journal = International Journal of Cancer | volume = 119 | issue = 4 | pages = 884–887 | publisher = Wiley-Liss, Inc | date = 2006-03-23 | url = http://www3.interscience.wiley.com/cgi-bin/abstract/112550783/ABSTRACT | doi = 10.1002/ijc.21903 | accessdate = 2006-10-09 | pmid=16557583 }}</ref> obesity,<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref> and environmental factors such as tobacco use and radiation.<ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>
Common risk factors in the development of [[breast]] cancer are [[family history]], dense breast, obesity, radiation therapy, older age at first birth or never having given birth, hormone replacement therapy, and alcohol.
 
==Common Risk Factor==
===Age===
===Family history===
The risk of getting breast cancer increases with age. A woman who lives to age 90 has a lifetime risk of about 14.3%, or one in seven.<ref>{{cite web | title = Individual Risk Factors| publisher = BreastCander.org | url = http://www.breastcancer.org/cmn_who_indrisk.html | accessdate = 2007-03-11}}</ref> The probability of breast cancer rises with age, but breast cancer tends to be more aggressive when it occurs in younger people.  One type of breast cancer that is especially aggressive and that occurs disproportionately in younger people is [[inflammatory breast cancer]]. It is initially [[cancer staging|staged]] as Stage IIIb or Stage IV. Also, it is unique because it often does not present a lump, so it is often undetected by [[mammography]] or [[medical ultrasonography|ultrasound]]. I[[Inflammatory breast cancer|nflammatory breast cancer]] is usually present with the signs and symptoms of a breast infection like [[mastitis]], and the treatment is usually a combination of surgery, radiation, and chemotherapy.
* Although less than 15 percent of women with breast cancer have a positive [[family history]], a woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter) with the history of breast cancer.
 
* Around 5-10 percent of breast cancers are due to inherited gene mutations either from one’s mother or father.
===Sex===
* ''[[BRCA1]]'' and ''[[BRCA2]] mutations'' are the most common genetic abnormality in breast cancer.<ref name="pmid15546503">Yoshida K, Miki Y (2004) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=15546503 Role of BRCA1 and BRCA2 as regulators of DNA repair, transcription, and cell cycle in response to DNA damage.] ''Cancer Sci'' 95 (11):866-71. PMID: [https://pubmed.gov/15546503 15546503]</ref>  
Men have a lower risk of developing breast cancer (approximately 1.08 per 100,000 men per year), however, this risk appears to be rising.<ref name="Giordano">{{cite journal | last = Giordano | first = Sharon H | authorlink = | coauthors = Cohen DS, Buzdar AU, Perkins G, Hortobagyi GN | title = Breast carcinoma in men | journal = Cancer | volume = 101 | issue = 1 | pages = 51-57 | publisher =American Cancer Society | date = May 2004 | url= http://www3.interscience.wiley.com/cgi-bin/fulltext/108565241/HTMLSTART | doi = | id = | accessdate = }}</ref>
:* Women with a [[BRCA1|''BRCA1'']] ''and''  [[BRCA2|''BRCA2'']] mutation have up to a 72% and 69% lifetime risk of developing breast cancer respectively.
 
:* Patients with [[BRCA1|''BRCA1'']] or [[BRCA2|''BRCA2'']] are often younger compared to their counterparts without these mutations.  
===Heredity===
:* There is also an increased risk of developing [[ovarian cancer]] risk in subjects with mutated ''[[BRCA1]]'' and''[[BRCA2]]''.
In 5% of breast cancer cases, there is a strongly inherited familial risk.<ref name="pmid9544766">{{cite journal |author=Malone KE, Daling JR, Thompson JD, O'Brien CA, Francisco LV, Ostrander EA |title=BRCA1 mutations and breast cancer in the general population: analyses in women before age 35 years and in women before age 45 years with first-degree family history |journal=JAMA |volume=279 |issue=12 |pages=922-9 |year=1998 |pmid=9544766 |doi=}}</ref>
:* Although ''[[BRCA1]]''mutations are barely correlated to breast cancer in men, a 6.8% increased risk of developing breast cancer has been observed in men with [[BRCA2|''BRCA2'']] mutations.
Two autosomal dominant [[gene]]s, ''[[BRCA1]]'' and ''[[BRCA2]]'', account for most of the cases of familial breast cancer. Family members who harbor mutations in these genes have a 60% to 80% risk of developing breast cancer in their lifetimes.<ref name="pmid9544766"/>  Other associated malignancies include [[ovarian cancer]] and [[pancreatic cancer]]. If a mother or a sister is diagnosed breast cancer, the risk of a hereditary ‘’’[[BRCA1]]’’’ or ‘’’[[BRCA2]]’’’ gene mutation is about 2-fold higher than that for women without a familial history. In addition to the BRCA genes associated with breast cancer, the presence of ''[[NBR2]]'', near breast cancer gene 1, has been discovered; research into its contribution to breast cancer pathogenesis is ongoing.<ref name="Beth Elton_2007">{{cite journal |author=Emilie Auriol, Lise-Marie Billard, Frederique Magdinier, Robert Dante |title=Specific binding of the methyl binding domain protein 2 at the ''BRCA1-NBR2'' locus |journal=Nucleic Acids Research |volume=33 |issue=13 |pages=4243-4254 |year=2005}}</ref>
* We should keep in mind that around 85% of women with breast cancers have no [[family history]].
Commercial testing for ‘’’[[BRCA1]]’’’ and ‘’’[[BRCA2]]’’’ gene mutations has been available since at least 2004.  Genetic testing for BRCA gene mutations is conducted exclusively by [[Myriad Genetics]], located in Salt Lake City.
* Sensitivity of commercial BRCA mutation tests like 23andMe is debated. For example 23andMe’s testing formula is based on solely three genetic variants, most prevalent among Ashkenazi Jews, while most people carry other mutations of the gene. This will result in false negative results. As accurately stated by Prof. Mary-Claire King, who discovered the BRCA1, ''“The F.D.A. should not have permitted this out-of-date approach to be used for medical purposes. Misleading, falsely reassuring results from their incomplete testing can cost women’s lives.”''
 
===Diet===
Dietary influences have been proposed and examined, and recent research suggests that low-fat diets may significantly decrease the risk of breast cancer as well as the recurrence of breast cancer.<ref>{{cite journal
  | author = Chlebowski RT, Blackburn GL, Thomson CA, Nixon DW, Shapiro A, Hoy MK, et al.
  | title = Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study (WINS).
  | journal =J Natl Cancer Inst
  | volume =98
  | issue =24
  | pages =1767-1776
  | pmid = 17179478
  | url =
}}</ref>
Another study showed no contribution of dietary fat intake on the incidence of breast cancer in over 300,000 women.<ref name="pmid8538706">{{cite journal |author=Hunter DJ, Spiegelman D, Adami HO, ''et al'' |title=Cohort studies of fat intake and the risk of breast cancer--a pooled analysis |journal=N. Engl. J. Med. |volume=334 |issue=6 |pages=356-61 |year=1996 |pmid=8538706 |doi=}}</ref>  A randomized controlled study of the consequences of a low-fat diet, the Women's Health Initiative, failed to show a [[statistical significance|statistically significant]] reduction in breast cancer incidence in the overall group assigned to a low-fat diet; the authors did, however, find evidence of a benefit in the subgoup of women who followed the low-fat diet in a strict manner.<ref name="pmid16467232">{{cite journal |author=Prentice RL, Caan B, Chlebowski RT, ''et al'' |title=Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial |journal=JAMA |volume=295 |issue=6 |pages=629-42 |year=2006 |pmid=16467232 |doi=10.1001/jama.295.6.629}}</ref> Another randomized trial, the Nurses' Health Study II, found increased breast cancer incidence in premenopausal women only, with higher intake of animal fat, but not vegetable fat. Taken as a whole, these results point to a possible association between dietary fat intake and breast cancer incidence, though these interactions are hard to measure in large groups of women.
 
In a study published in the ''Journal of the American Medical Association'', biomedical investigators found that Brassica vegetable intake (broccoli, cauliflower, cabbage, kale and Brussels sprouts) was inversely related to breast cancer development. The relative risk among women in the highest decile of Brassica vegetable consumption (median, 1.5 servings per day) compared to the lowest decile (virtually no consumption) was 58%. That is, women who consumed the most Brassica vegetables were 58% less likely to develop breast cancer.<ref>{{cite journal |author=Terry P, Wolk A, Persson I, Magnusson C title = Brassica Vegetables and Breast Cancer Risk |journal=JAMA |volume=285 |issue=23 |pages=2975-2976 |year=2001}}</ref>
 
A significant environmental effect is likely responsible for the different rates of breast cancer incidence between countries with different dietary customs. Researchers have long measured that breast cancer rates in an immigrant population soon come to resemble the rates of the host country after a few generations.  The reason for this is speculated to be immigrant uptake of the host country diet.  The prototypical example of this phenomenon is the changing rate of breast cancer in Japanese immigrants after their arrival in America.<ref>{{cite journal |author= Nelson N title = Migrant Studies Aid Search for Factors Linked to Breast Cancer Risk |journal=JAMA |volume=8 |issue=7 |pages=436-438 |year=2006}}</ref>
 
===Alcohol Consumption===
Alcohol appears to increase the risk of breast cancer, though meaningful increases are limited to higher alcohol intake levels. Breast cancer constitutes about 7.3% of all cancers.<ref name=ACS_2007>{{cite web | title = Statistics for 2007 | publisher = American Cancer Society | url = http://www.cancer.org/docroot/stt/stt_0.asp | accessdate = 2007-03-11}}</ref> Among women, breast cancer comprises 60% of alcohol-attributable cancers.<ref name=Boffetta_2006>{{cite journal
  | last = Boffetta
  | first = Paolo
  | coauthors = Hashibe, Mia; La Vecchia, Carlo; Zatonski, Witold; Rehm, Jürgen
  | title = The burden of cancer attributable to alcohol drinking
  | journal = International Journal of Cancer
  | volume = 119
  | issue = 4
  | pages = 884–887
  | publisher = Wiley-Liss, Inc
  | date = 2006-03-23
  | url = http://www3.interscience.wiley.com/cgi-bin/abstract/112550783/ABSTRACT
  | doi = 10.1002/ijc.21903
  | accessdate = 2006-10-09
  | pmid=16557583 }}</ref> The UK's ''Review of Alcohol: Association with Breast Cancer'' concludes that "studies confirm previous observations that there appears to be an association between alcohol intake and increased risk of breast cancer in women. On balance, there was a weak association between the amount of alcohol consumed and the relative risk."<ref name=UKDOH_Alcohol>{{cite web | title = Review of Alcohol: Association with Breast Cancer | publisher = U.K. Dept. of Health | url = http://www.advisorybodies.doh.gov.uk/pdfs/alcbrrev.pdf | accessdate = 2007-03-11}}</ref>
 
The National Institute on Alcohol Abuse and Alcoholism (NIAAA) concludes that "Chronic alcohol consumption has been associated with a small (averaging 10 percent) increase in a woman's risk of breast cancer."<ref name=Friedenreich_1993>{{cite journal |author=Friedenreich C, Howe G, Miller A, Jain M |title=A cohort study of alcohol consumption and risk of breast cancer |journal=Am J Epidemiol |volume=137 |issue=5 |pages=512-20 |year=1993 |pmid=8465803}}</ref><ref name=Longnecker_1988>{{cite journal |author=Longnecker M, Berlin J, Orza M, Chalmers T |title=A meta-analysis of alcohol consumption in relation to risk of breast cancer |journal=JAMA |volume=260 |issue=5 |pages=652-6 |year=1988 |pmid=3392790}}</ref><ref name=Longnecker_1992>{{cite journal | author=Longnecker MP | title = Alcohol consumption in relation to risk of cancers of the breast and large bowel | journal = Alcohol Health & Research World | year = 1992 | volume = 16 | issue = 3 | pages = 223-229 | url= }}</ref><ref name=Nasca_1990>{{cite journal |author=Nasca P, Baptiste M, Field N, Metzger B, Black M, Kwon C, Jacobson H |title=An epidemiological case-control study of breast cancer and alcohol consumption |journal=Int J Epidemiol |volume=19 |issue=3 |pages=532-8 |year=1990 |pmid=2262245}}</ref> According to these studies, the risk appears to increase as the quantity and duration of alcohol consumption increases.Other studies, however, have found no evidence of such a link. <ref name=Chu_1989>{{cite journal |author=Chu S, Lee N, Wingo P, Webster L |title=Alcohol consumption and the risk of breast cancer |journal=Am J Epidemiol |volume=130 |issue=5 |pages=867-77 |year=1989 |pmid=2683749}}</ref><ref name=Schatzkin_1989>{{cite journal |author=Schatzkin A, Piantadosi S, Miccozzi M, Bartee D |title=Alcohol consumption and breast cancer: a cross-national correlation study |journal=Int J Epidemiol |volume=18 |issue=1 |pages=28-31 |year=1989 |pmid=2722377}}</ref><ref name=Webster_1983>{{cite journal |author=Webster L, Layde P, Wingo P, Ory H |title=Alcohol consumption and risk of breast cancer |journal=Lancet |volume=2 |issue=8352 |pages=724-6 |year=1983 |pmid=6136850}}</ref>
 
The ''Committee on Carcinogenicity of Chemicals in Food, Consumer Products Non-Technical Summary'' concludes that, "the new research estimates that a woman drinking an average of two units of alcohol per day has a lifetime risk of developing breast cancer 8% higher than a woman who drinks an average of one unit of alcohol per day.<ref name=UKDOH_Chemicals>{{cite web | title = CONSUMPTION OF ALCOHOLIC BEVERAGES AND RISK OF BREAST CANCER IN WOMEN | publisher = U.K. Dept. of Health | url = http://www.advisorybodies.doh.gov.uk/pdfs/alco04nontech.pdf | accessdate = 2007-03-11}}</ref> The risk of breast cancer further increases with each additional drink consumed per day. The research also concludes that approximately 6% (between 3.2% and 8.8%) of breast cancers reported in the UK each year could be prevented if drinking was reduced to a very low level (i.e. less than 1 unit/week)." A review article from JAMA also found that breast cancer incidence seems to increase with increasing alcohol consumption.<ref name="pmid11694156">{{cite journal |author=Singletary KW, Gapstur SM |title=Alcohol and breast cancer: review of epidemiologic and experimental evidence and potential mechanisms |journal=JAMA |volume=286 |issue=17 |pages=2143-51 |year=2001 |pmid=11694156 |doi=}}</ref> It has been reported that "two drinks daily increase the risk of getting breast cancer by about 25 percent" (NCI), but the evidence is inconsistent. The Framingham study has carefully tracked individuals since the 1940s. Data from that research found that drinking alcohol moderately did not increase breast cancer risk (Wellness Facts). Similarly, research by the Danish National Institute for Public Health found that moderate drinking had virtually no effect on breast cancer risk.<ref name=Petri_2004>{{cite journal |author=Petri A, Tjønneland A, Gamborg M, Johansen D, Høidrup S, Sørensen T, Grønbaek M |title=Alcohol intake, type of beverage, and risk of breast cancer in pre- and postmenopausal women |journal=Alcohol Clin Exp Res |volume=28 |issue=7 |pages=1084-90 |year=2004 |pmid=15252295}}</ref>
 
One study suggests that women who frequently drink red wine may have an increased risk of developing breast cancer.<ref name=Maggiolini_2005>{{cite journal |author=Maggiolini M, Recchia A, Bonofiglio D, Catalano S, Vivacqua A, Carpino A, Rago V, Rossi R, Andò S |title=The red wine phenolics piceatannol and myricetin act as agonists for estrogen receptor alpha in human breast cancer cells |journal=J Mol Endocrinol |volume=35 |issue=2 |pages=269-81 |year=2005 |pmid=16216908}}</ref>
 
"Folate intake counteracts breast cancer risk associated with alcohol consumption"<ref>Mayo Clinic news release [[June 26]] 2001 [http://www.mayoclinic.org/news2001-rst/857.html "Folate Intake Counteracts Breast Cancer Risk Associated with Alcohol Consumption"]</ref> and "women who drink alcohol and have a high folate intake are not at increased risk of cancer."<ref>Boston University [http://www.bu.edu/act/alcoholandhealth/issues/issue_may04/html/04-0506-ellison_baily.html ''Folate, Alcohol, and Cancer Risk'']</ref> Those who have a high (200 micrograms or more per day) level of [[folate]] (folic acid or Vitamin B9) in their diet are not at increased risk of breast cancer compared to those who abstain from alcohol.<ref name=Zhang_1999>{{cite journal |author=Zhang S, Hunter D, Hankinson S, Giovannucci E, Rosner B, Colditz G, Speizer F, Willett W |title=A prospective study of folate intake and the risk of breast cancer |journal=JAMA |volume=281 |issue=17 |pages=1632-7 |year=1999 |pmid=10235158}}</ref> Foods rich in folate include citrus fruits, citrus juices, dark green leafy vegetables (such as spinach), dried beans, and peas. Vitamin B9 can also be taken in a multivitamin pill.
 
===Obesity===
Gaining weight after menopause can increase a woman's risk. A recent study found that putting on 9.9kg (22lbs) after menopause increased the risk of developing breast cancer by 18%.<ref>BBC report [http://news.bbc.co.uk/1/hi/health/5171838.stm Weight link to breast cancer risk]</ref>
 
===Hormones===
Persistently increased blood levels of [[estrogen]] are associated with an increased risk of breast cancer, as are increased levels of the [[androgens]] [[androstenedione]] and [[testosterone]] (which can be directly converted by [[aromatase]] to the estrogens [[estrone]] and [[estradiol]], respectively). Increased blood levels of [[progesterone]] are associated with a decreased risk of breast cancer in premenopausal women.<ref>{{cite journal |author=Yager JD |coauthors=Davidson NE |title=Estrogen carcinogenesis in breast cancer |journal=New Engl J Med |volume=354 |issue=3 |year=2006 |pages=270-82 |id=PMID 16421368}}</ref> A number of circumstances which increase exposure to endogenous estrogens, including not having children, delaying first childbirth, not breastfeeding, early [[menarche]] (the first menstrual period) and late [[menopause]] are suspected of increasing lifetime risk for developing breast cancer.<ref>American Cancer Society. ([[2006-10-03]]). [http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_breast_cancer_5.asp What Are the Risk Factors for Breast Cancer?] Retrieved [[2006-03-30]].</ref>
 
[[Hormonal contraception|Hormonal contraceptives]] may produce a slight increase in the risk of breast cancer diagnosis among current and recent users, but this appears to be a short-term effect. In 1996, the largest collaborative reanalysis of individual data on over 150,000 women in 54 studies of breast cancer found a [[relative risk]] (RR) of 1.24 among current [[combined oral contraceptive pill]] users; 10 or more years after stopping, no difference was seen. Furthermore, the cancers diagnosed in women who had ever used hormonal contraceptives were less advanced than those in nonusers, raising the possibility that the small excess among users was due to increased detection.<!--
--><ref name="oxford 1996a">{{cite journal |author=Collaborative Group on Hormonal Factors in Breast Cancer |year=1996 |title=Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53,297 women with breast cancer and 100,239 women without breast cancer from 54 epidemiological studies |journal=[[The Lancet|Lancet]] |volume=347 |issue=9017 |pages=1713-27 |id=PMID 8656904}}</ref><!--
--><ref name="oxford 1996b">{{cite journal |author=Collaborative Group on Hormonal Factors in Breast Cancer |year=1996 |title=Breast cancer and hormonal contraceptives: further results |journal=Contraception |volume=54 |issue=3 Suppl |pages=1S-106S |id=PMID 8899264}}</ref> The relative risk of breast cancer diagnosis associated with current and recent use of hormonal contraceptives did not appear to vary with family history of breast cancer.<ref name=hormone>{{cite web |url=http://www.cancer.gov/cancertopics/pdq/genetics/breast-and-ovarian/healthprofessional#Section_340 |title=Hormone Therapy |accessdate=2006-08-12 |author=National Cancer Institute |date=2006-08-03 |work=Genetics of Breast and Ovarian Cancer}}</ref>
 
Data exists from both observational and [[randomized clinical trial]]s regarding the association between postmenopausal [[hormone replacement therapy]] (HRT) and breast cancer. The largest meta-analysis (1997) of data from 51 observational studies, indicated a relative risk of breast cancer of 1.35 for women who had used HRT for 5 or more years after menopause. The estrogen-plus-[[progestin]] arm of the [[Women's Health Initiative]] (WHI), a randomized controlled trial, which randomized more than 16,000 postmenopausal women to receive combined hormone therapy or placebo, was halted early (2002) because health risks exceeded benefits. One of the adverse outcomes prompting closure was a significant increase in both total and invasive breast cancers (RR = 1.24) in women randomized to receive estrogen and progestin for an average of 5 years. HRT-related breast cancers had adverse prognostic characteristics (more advanced stages and larger tumors) compared with cancers occurring in the placebo group, and HRT was also associated with a substantial increase in abnormal mammograms. Short-term use of hormones for treatment of menopausal symptoms appears to confer little or no breast cancer risk.<ref name=hormone>{{cite web |url=http://www.cancer.gov/cancertopics/pdq/genetics/breast-and-ovarian/healthprofessional#Section_340 |title=Hormone Therapy |accessdate=2006-08-12 |author=National Cancer Institute |date=2006-08-03 |work=Genetics of Breast and Ovarian Cancer}}</ref>


===Environmental risk factors===
'''A personal history of breast cancer or benign (noncancer) breast disease'''<ref name="CRF">Breast Cancer. National Cancer Institute (2016) http://www.cancer.gov/types/breast/patient/breast-prevention-pdq#section/_12 Accessed on January 15, 2016 </ref>
*Women with any of the following have an increased risk of breast cancer:
:*A personal history of invasive breast cancer, ductal [[carcinoma in situ]] (DCIS), or lobular carcinoma in situ (LCIS).
:*A personal history of benign (noncancer) breast disease.
'''A family history of breast cancer'''
*Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.<ref name="pmid28578505">Brewer HR, Jones ME, Schoemaker MJ, Ashworth A, Swerdlow AJ (2017) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=28578505 Family history and risk of breast cancer: an analysis accounting for family structure.] ''Breast Cancer Res Treat'' 165 (1):193-200. [http://dx.doi.org/10.1007/s10549-017-4325-2 DOI:10.1007/s10549-017-4325-2] PMID: [https://pubmed.gov/28578505 28578505]</ref>
'''Inherited gene changes'''
*Women who have inherited changes in the ''[[BRCA1]]'' and ''[[BRCA2]]'' genes or in certain other genes have a higher risk of breast cancer, ovarian cancer, and maybe colon cancer.
:*The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.
*Men who have inherited certain changes in the ''[[BRCA2]]'' gene have a higher risk of breast, [[Prostate cancer|prostate]], and [[pancreatic cancer]]<nowiki/>s, and [[lymphoma]].
'''Dense breasts'''
*Having breast tissue that is dense on a mammogram is a factor in breast cancer risk.<ref name="pmid25763718">Freer PE (2015) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=25763718 Mammographic breast density: impact on breast cancer risk and implications for screening.] ''Radiographics'' 35 (2):302-15. [http://dx.doi.org/10.1148/rg.352140106 DOI:10.1148/rg.352140106] PMID: [https://pubmed.gov/25763718 25763718]</ref>
:*The level of risk depends on how dense the breast tissue is.
:*Women with very dense breasts have a higher risk of breast cancer than women with low breast density.
:*Increased breast density is often an inherited trait, but it may also occur in women who:
::*Have not had children
::*Have the first pregnancy late in life
::*Take postmenopausal hormones (HRT)
::*Drink alcohol
'''Exposure of breast tissue to estrogen made in the body'''
*Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.<ref name="pmid20104523">Yue W, Wang JP, Li Y, Fan P, Liu G, Zhang N et al. (2010) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=20104523 Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms.] ''Int J Cancer'' 127 (8):1748-57. [http://dx.doi.org/10.1002/ijc.25207 DOI:10.1002/ijc.25207] PMID: [https://pubmed.gov/20104523 20104523]</ref>
*A woman's exposure to estrogen is increased in the following ways:
:*Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
:*Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
:*Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.
'''Taking hormone therapy for symptoms of menopause'''
*Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.<ref name="pmid21253794">Howell A, Evans GD (2011) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=21253794 Hormone replacement therapy and breast cancer.] ''Recent Results Cancer Res'' 188 ():115-24. [http://dx.doi.org/10.1007/978-3-642-10858-7_10 DOI:10.1007/978-3-642-10858-7_10] PMID: [https://pubmed.gov/21253794 21253794]</ref>
'''Radiation therapy to the breast or chest'''
*Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given.<ref name="pmid19930978">Ng AK, Travis LB (2009) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=19930978 Radiation therapy and breast cancer risk.] ''J Natl Compr Canc Netw'' 7 (10):1121-8. PMID: [https://pubmed.gov/19930978 19930978]</ref> The risk is highest if radiation treatment was used during puberty when breasts are forming.
*Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.
*For women who have inherited changes in the''[[BRCA1]]'' and ''[[BRCA2]]'' genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.
'''Obesity'''
*Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.<ref name="pmid28763097">Picon-Ruiz M, Morata-Tarifa C, Valle-Goffin JJ, Friedman ER, Slingerland JM (2017) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=28763097 Obesity and adverse breast cancer risk and outcome: Mechanistic insights and strategies for intervention.] ''CA Cancer J Clin'' 67 (5):378-397. [http://dx.doi.org/10.3322/caac.21405 DOI:10.3322/caac.21405] PMID: [https://pubmed.gov/28763097 28763097]</ref>
'''Drinking alcohol'''
*Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.<ref name="pmid24265860">McDonald JA, Goyal A, Terry MB (2013) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=24265860 Alcohol Intake and Breast Cancer Risk: Weighing the Overall Evidence.] ''Curr Breast Cancer Rep'' 5 (3):. [http://dx.doi.org/10.1007/s12609-013-0114-z DOI:10.1007/s12609-013-0114-z] PMID: [https://pubmed.gov/24265860 24265860]</ref>
==Less Common Risk Factors==
====Tobacco====
====Tobacco====
Most studies have not found an increased risk of breast cancer from active [[tobacco smoking]], although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to [[passive smoking|secondhand smoke]] compared to women who reported no exposure to secondhand smoke.<ref name="acs bc facts 2005-6"/>
*Most studies have not found an increased risk of breast cancer from active [[tobacco smoking]], although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to [[passive smoking|secondhand smoke]] compared to women who reported no exposure to secondhand smoke.<ref name="acs bc facts 2005-6" />


====Radiation====
====Radiation====
Women who have received high-dose [[ionizing radiation]] to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.<!--
*Women who have received high-dose [[ionizing radiation]] to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.<!--
   --><ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>
   --><ref name="acs bc facts 2005-6">{{cite web |author=[[American Cancer Society|ACS]] |year=2005 |title=Breast Cancer Facts & Figures 2005-2006 |url=http://www.cancer.org/downloads/STT/CAFF2005BrFacspdf2005.pdf |accessdate=2007-04-26}}</ref>
*Serial mammography might slightly increase the risk of developing breast cancer in high-risk patients such as patients with a family history of breast cancer and patients with known genetic carcinogenic mutations.
:*According to a recently published study by Jansen-van der Weide et.al. average increased the risk of breast cancer because of low-dose radiation exposure was  (OR between 1.3 and 2 with respect to the patients' risk and exposure) observed compared to that of high-risk women not exposed to low-dose radiation.<ref name="pmid20582702">Jansen-van der Weide MC, Greuter MJ, Jansen L, Oosterwijk JC, Pijnappel RM, de Bock GH (2010) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=20582702 Exposure to low-dose radiation and the risk of breast cancer among women with a familial or genetic predisposition: a meta-analysis.] ''Eur Radiol'' 20 (11):2547-56. [http://dx.doi.org/10.1007/s00330-010-1839-y DOI:10.1007/s00330-010-1839-y] PMID: [https://pubmed.gov/20582702 20582702]</ref>
:* Pooled OR revealed an increased risk of breast cancer among high-risk women due to low-dose radiation exposure (OR = 1.3, 95% CI: 0.9- 1.8).
:* Exposure before age 20 (OR = 2.0, 95% CI: 1.3-3.1)
:* A mean of ≥5 exposures (OR = 1.8, 95% CI: 1.1-3.0)
:* When using low-dose radiation among high-risk women, a careful approach is needed, by means of
:*They recommended careful approach in these subgroup of patients as follows:
::*Reducing repeated exposure,
::*Avoidance of exposure at a younger age
:;*Using non-ionising screening techniques.
:*According to another study by Diana L. Miglioretti et.al. radiation-induced breast cancer incidence and mortality from digital mammography screening are impacted by:<ref name="pmid26756460">Miglioretti DL, Lange J, van den Broek JJ, Lee CI, van Ravesteyn NT, Ritley D et al. (2016) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=26756460 Radiation-Induced Breast Cancer Incidence and Mortality From Digital Mammography Screening: A Modeling Study.] ''Ann Intern Med'' 164 (4):205-14. [http://dx.doi.org/10.7326/M15-1241 DOI:10.7326/M15-1241] PMID: [https://pubmed.gov/26756460 26756460]</ref>
::*Dose variability from screening and resultant diagnostic work-up,
::*Initiation age
::*Screening frequency.
::*Women with large breasts may be at higher risk of radiation-induced breast cancer;
*'''''However, we should keep in mind that "the benefits of screening outweigh these risks".'''''


====Impact of environmental estrogenic mimics====
====Impact of environmental estrogenic mimics====
Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds, including chemicals used in pesticides, cosmetics and cleaning products, contribute to the development of breast cancer.
*Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals, and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds, including chemicals used in pesticides, cosmetics, and cleaning products, contribute to the development of breast cancer.
A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.<ref>{{cite news | author = Ctv.Ca News Staff | title= Breast cancer more likely in farm workers: study |url= http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20061012/breastcancer_farming_061012/20061012?hub=Health| publisher= Ctv.Ca |date=2006-10-12 |accessdate=2007-03-11 }}</ref>
*A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.<ref>{{cite news | author = Ctv.Ca News Staff | title= Breast cancer more likely in farm workers: study |url= http://www.ctv.ca/servlet/ArticleNews/story/CTVNews/20061012/breastcancer_farming_061012/20061012?hub=Health| publisher= Ctv.Ca |date=2006-10-12 |accessdate=2007-03-11 }}</ref>
The increasing prevalence of these substances in the environment may explain the rising incidence of breast cancer, though direct evidence is sparse.
The increasing prevalence of these substances in the environment may explain the rising incidence of breast cancer, though direct evidence is sparse.


====Dioxins====
====Dioxins====
Although not well-quantified, there has long been a concern about risk associated with environmental estrogenic compounds, such as [[dioxins]]. {{Fact|date=June 2007}}
*Although not well-quantified, there has long been a concern about the risk associated with environmental estrogenic compounds, such as [[dioxins]]. <ref name="pmid25849111">Danjou AM, Fervers B, Boutron-Ruault MC, Philip T, Clavel-Chapelon F, Dossus L (2015) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=25849111 Estimated dietary dioxin exposure and breast cancer risk among women from the French E3N prospective cohort.] ''Breast Cancer Res'' 17 ():39. [http://dx.doi.org/10.1186/s13058-015-0536-9 DOI:10.1186/s13058-015-0536-9] PMID: [https://pubmed.gov/25849111 25849111]</ref><ref name="pmid12117637">Warner M, Eskenazi B, Mocarelli P, Gerthoux PM, Samuels S, Needham L et al. (2002) [https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=12117637 Serum dioxin concentrations and breast cancer risk in the Seveso Women's Health Study.] ''Environ Health Perspect'' 110 (7):625-8. [http://dx.doi.org/10.1289/ehp.02110625 DOI:10.1289/ehp.02110625] PMID: [https://pubmed.gov/12117637 12117637]</ref>


====Light levels====
====Light levels====
Researchers at the [[National Cancer Institute]] and [[National Institute of Environmental Health Sciences]] have conducted a study that suggests that artificial light during the night can be a factor for breast cancer.<ref>''The Independent'' [http://news.independent.co.uk/uk/health_medical/article1090208.ece Avoid breast cancer. Sleep in the dark...]</ref>
*Researchers at the [[National Cancer Institute]] and [[National Institute of Environmental Health Sciences]] have conducted a study that suggests that artificial light during the night can be a factor for breast cancer.<ref>''The Independent'' [http://news.independent.co.uk/uk/health_medical/article1090208.ece Avoid breast cancer. Sleep in the dark...]</ref>
 
===Viral breast cancer pathogenesis research===
Humans are not the only mammals susceptible to breast cancer.  Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the [[mouse mammary tumour virus]] (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis.  This finding is taken to mean that a viral [[etiology]] of human breast cancer is at least possible, though there is no definitive evidence to support the claim that MMTV causes human breast cancer.  For example, there may be critical differences between cancer pathogenesis in mice and people.  The understanding of the role of MMTV or other viruses in human breast cancer is preliminary as of May 2007.
 
===Factors with minimal or no impact on breast cancer risk===
====Abortion====
Studies on rats<ref name="RUSSO3">{{cite journal |author=Russo J, Russo I |title=Biological and molecular bases of mammary carcinogenesis |journal=Lab Invest |volume=57 |issue=2 |pages=112-37 |year=1987 |pmid=3302534}}</ref> have led to speculation that [[abortion]] may increase the risk of breast cancer because of the hormones that initiate breast tissue growth in early pregnancy. Some early interview<ref name="DALING">Daling J.R. ''et al.'' (1994) [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=7932822 PubMed] ''Risk of breast cancer among young women: relationship to induced abortion.'' J Natl Cancer Inst. 1994 Nov 2;86(21):1584-92.</ref> and record<ref name="HOWE">{{cite journal | author = Howe H, Senie R, Bzduch H, Herzfeld P | title = Early abortion and breast cancer risk among women under age 40. | journal = Int J Epidemiol | volume = 18 | issue = 2 | pages = 300-4 | year = 1989 | id = PMID 2767842}}</ref> based [[case-control]] studies indicated a possible correlation; however, more recent record based studies<ref name="MELBYE">{{cite journal |author=Melbye M, Wohlfahrt J, Olsen J, Frisch M, Westergaard T, Helweg-Larsen K, Andersen P |title=Induced abortion and the risk of breast cancer |journal=N Engl J Med |volume=336 |issue=2 |pages=81-5 |year=1997 |pmid=8988884}}</ref><ref name="epic">{{cite journal |author=Reeves G, Kan S, Key T, Tjønneland A, Olsen A, Overvad K, Peeters P, Clavel-Chapelon F, Paoletti X, Berrino F, Krogh V, Palli D, Tumino R, Panico S, Vineis P, Gonzalez C, Ardanaz E, Martinez C, Amiano P, Quiros J, Tormo M, Khaw K, Trichopoulou A, Psaltopoulou T, Kalapothaki V, Nagel G, Chang-Claude J, Boeing H, Lahmann P, Wirfält E, Kaaks R, Riboli E |title=Breast cancer risk in relation to abortion: Results from the EPIC study |journal=Int. J. Cancer |volume=119 |issue=7 |pages=1741-5 |year=2006 |pmid=16646050}}</ref><ref name="harvard">Karin B. Michels, ScD, PhD; Fei Xue, MD; Graham A. Colditz, MD, DrPH; Walter C. Willett, MD, DrPH. "Induced and Spontaneous Abortion and Incidence of Breast Cancer Among Young Women." ''Arch Intern Med.'' 2007;167:814-820. [http://archinte.ama-assn.org/cgi/content/short/167/8/814 Abstract].</ref> and a large [[meta-analysis]]<ref>Beral V, Bull D et al, "Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,000 women with breast cancer from 16 countries." ''Lancet,'' 2004 Mar 27;363(9414):1007-16 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?itool=abstractplus&db=pubmed&cmd=Retrieve&dopt=abstractplus&list_uids=15051280 PMID 15051280]</ref> study do not support this association. The topic was examined by a [[National Cancer Institute]] (NCI) workshop in 2003, in response to the Bush Administration's alteration of the NCI's website to emphasize studies indicating a potential link.<ref>[http://oversight.house.gov/features/politics_and_science/example_breast_cancer.htm Politics and Science: Breast Cancer Risk]. Accessed [[July 23]] [[2007]].</ref> The NCI expert panel concluded, with the strongest level of evidence, that induced abortion is not associated with an increased risk of breast cancer.<ref>[http://www.cancer.gov/cancerinfo/ere-workshop-report Summary Report: Early Reproductive Events and Breast Cancer Workshop], from the U.S. [[National Cancer Institute]]. Posted [[March 4]] [[2003]]; accessed [[July 23]] [[2007]].</ref>
 
====Deodorants====
Much has been made of the possible contribution of aluminum-containing underarm antiperspirants to the incidence of breast cancer, since the most common location of a breast cancer is the upper outer quadrant of the breast.  [[Aluminum]] salts, such as those used in anti-perspirants, have recently been classified as metalloestrogens. In research published in the ''Journal of Applied Toxicology'', Dr. Philippa D. Darbre of the University of Reading has shown that aluminum salts increase estrogen-related gene expression in human breast cancer cells grown in the laboratory.<ref>Harding, Anne. (2006) [http://www.cancerpage.com/news/article.asp?id=9466 Aluminum Salts Could Increase Breast Cancer Risk]. Reuters Health.</ref><ref>{{cite journal
  | last =Darbre
  | first =PD
  | title =Metalloestrogens: an emerging class of inorganic xenoestrogens with potential to add to the oestrogenic burden of the human breast.
  | journal =Journal of Applied Toxicology
  | volume =26
  | issue =3
  | pages =191-7
  | publisher =John Wiley And Sons
  | date =2006 
  | pmid = 16489580
  | url =
}}</ref><ref>{{cite journal
  | last =Darbre
  | first =PD
  | title =Aluminium, antiperspirants and breast cancer.
  | journal =Journal of Inorganic Biochemistry
  | volume =99
  | issue =9
  | pages =1912-9
  | publisher =Elsevier
  | date = 2005
  | pmid=16045991mmmmmmiii
  | url =
}}</ref>
Fortunately, this ''in-vitro'' association between aluminum salts and estrogen activity does not translate into an increased risk of breast cancer in humans. The lack of association between underarm deodorants and breast cancer has been the subject of a number of research articles.<ref name="pmid14991030">{{cite journal |author=Surendran A |title=Studies linking breast cancer to deodorants smell rotten, experts say |journal=Nat. Med. |volume=10 |issue=3 |pages=216 |year=2004 |pmid=14991030 |doi=10.1038/nm0304-216b}}</ref><ref name="pmid12543590">{{cite journal |author= |title=Antiperspirants don't cause breast cancer |journal=Harvard women's health watch |volume=10 |issue=5 |pages=7 |year=2003 |pmid=12543590 |doi=}}</ref>
 
====Fertility treatments====
There is no persuasive connection between fertility medications and breast cancer.<ref>{{cite journal |author=Potashnik G, Lerner-Geva L, Genkin L, Chetrit A, Lunenfeld E, Porath A |title=Fertility drugs and the risk of breast and ovarian cancers: results of a long-term follow-up study |journal=Fertil. Steril. |volume=71 |issue=5 |pages=853-9 |year=1999 |pmid=10231045 |doi=}}</ref>
==References==
==References==
{{Reflist|2}}
{{Reflist|2}}
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[[Category:Mature chapter]]
[[Category:Oncology]]


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Latest revision as of 14:37, 22 April 2019


Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2] Mirdula Sharma, MBBS [3]

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Overview

Common risk factors in the development of breast cancer are family history, dense breast, obesity, radiation therapy, older age at first birth or never having given birth, hormone replacement therapy, and alcohol.

Common Risk Factor

Family history

  • Although less than 15 percent of women with breast cancer have a positive family history, a woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter) with the history of breast cancer.
  • Around 5-10 percent of breast cancers are due to inherited gene mutations either from one’s mother or father.
  • BRCA1 and BRCA2 mutations are the most common genetic abnormality in breast cancer.[1]
  • Women with a BRCA1 and BRCA2 mutation have up to a 72% and 69% lifetime risk of developing breast cancer respectively.
  • Patients with BRCA1 or BRCA2 are often younger compared to their counterparts without these mutations.
  • There is also an increased risk of developing ovarian cancer risk in subjects with mutated BRCA1 andBRCA2.
  • Although BRCA1mutations are barely correlated to breast cancer in men, a 6.8% increased risk of developing breast cancer has been observed in men with BRCA2 mutations.
  • We should keep in mind that around 85% of women with breast cancers have no family history.
  • Sensitivity of commercial BRCA mutation tests like 23andMe is debated. For example 23andMe’s testing formula is based on solely three genetic variants, most prevalent among Ashkenazi Jews, while most people carry other mutations of the gene. This will result in false negative results. As accurately stated by Prof. Mary-Claire King, who discovered the BRCA1, “The F.D.A. should not have permitted this out-of-date approach to be used for medical purposes. Misleading, falsely reassuring results from their incomplete testing can cost women’s lives.”

A personal history of breast cancer or benign (noncancer) breast disease[2]

  • Women with any of the following have an increased risk of breast cancer:
  • A personal history of invasive breast cancer, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).
  • A personal history of benign (noncancer) breast disease.

A family history of breast cancer

  • Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.[3]

Inherited gene changes

  • Women who have inherited changes in the BRCA1 and BRCA2 genes or in certain other genes have a higher risk of breast cancer, ovarian cancer, and maybe colon cancer.
  • The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.

Dense breasts

  • Having breast tissue that is dense on a mammogram is a factor in breast cancer risk.[4]
  • The level of risk depends on how dense the breast tissue is.
  • Women with very dense breasts have a higher risk of breast cancer than women with low breast density.
  • Increased breast density is often an inherited trait, but it may also occur in women who:
  • Have not had children
  • Have the first pregnancy late in life
  • Take postmenopausal hormones (HRT)
  • Drink alcohol

Exposure of breast tissue to estrogen made in the body

  • Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.[5]
  • A woman's exposure to estrogen is increased in the following ways:
  • Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
  • Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
  • Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.

Taking hormone therapy for symptoms of menopause

  • Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.[6]

Radiation therapy to the breast or chest

  • Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given.[7] The risk is highest if radiation treatment was used during puberty when breasts are forming.
  • Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.
  • For women who have inherited changes in theBRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.

Obesity

  • Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.[8]

Drinking alcohol

  • Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.[9]

Less Common Risk Factors

Tobacco

  • Most studies have not found an increased risk of breast cancer from active tobacco smoking, although a number of studies suggest an increased risk of breast cancer in both active smokers and those exposed to secondhand smoke compared to women who reported no exposure to secondhand smoke.[10]

Radiation

  • Women who have received high-dose ionizing radiation to the chest (for example, as treatments for other cancers) have a relative risk of breast cancer between 2.1 to 4.0.[10]
  • Serial mammography might slightly increase the risk of developing breast cancer in high-risk patients such as patients with a family history of breast cancer and patients with known genetic carcinogenic mutations.
  • According to a recently published study by Jansen-van der Weide et.al. average increased the risk of breast cancer because of low-dose radiation exposure was (OR between 1.3 and 2 with respect to the patients' risk and exposure) observed compared to that of high-risk women not exposed to low-dose radiation.[11]
  • Pooled OR revealed an increased risk of breast cancer among high-risk women due to low-dose radiation exposure (OR = 1.3, 95% CI: 0.9- 1.8).
  • Exposure before age 20 (OR = 2.0, 95% CI: 1.3-3.1)
  • A mean of ≥5 exposures (OR = 1.8, 95% CI: 1.1-3.0)
  • When using low-dose radiation among high-risk women, a careful approach is needed, by means of
  • They recommended careful approach in these subgroup of patients as follows:
  • Reducing repeated exposure,
  • Avoidance of exposure at a younger age
  • Using non-ionising screening techniques.
  • According to another study by Diana L. Miglioretti et.al. radiation-induced breast cancer incidence and mortality from digital mammography screening are impacted by:[12]
  • Dose variability from screening and resultant diagnostic work-up,
  • Initiation age
  • Screening frequency.
  • Women with large breasts may be at higher risk of radiation-induced breast cancer;
  • However, we should keep in mind that "the benefits of screening outweigh these risks".

Impact of environmental estrogenic mimics

  • Although environmental exposures are not generally cited as risk factors for the disease (except for diet, pharmaceuticals, and radiation), a substantial and growing body of evidence indicates that exposures to certain toxic chemicals and hormone-mimicking compounds, including chemicals used in pesticides, cosmetics, and cleaning products, contribute to the development of breast cancer.
  • A recent Canadian study concluded that female farm workers are three times more likely to have breast cancer.[13]

The increasing prevalence of these substances in the environment may explain the rising incidence of breast cancer, though direct evidence is sparse.

Dioxins

  • Although not well-quantified, there has long been a concern about the risk associated with environmental estrogenic compounds, such as dioxins. [14][15]

Light levels

References

  1. ↑ Yoshida K, Miki Y (2004) Role of BRCA1 and BRCA2 as regulators of DNA repair, transcription, and cell cycle in response to DNA damage. Cancer Sci 95 (11):866-71. PMID: 15546503
  2. ↑ Breast Cancer. National Cancer Institute (2016) http://www.cancer.gov/types/breast/patient/breast-prevention-pdq#section/_12 Accessed on January 15, 2016
  3. ↑ Brewer HR, Jones ME, Schoemaker MJ, Ashworth A, Swerdlow AJ (2017) Family history and risk of breast cancer: an analysis accounting for family structure. Breast Cancer Res Treat 165 (1):193-200. DOI:10.1007/s10549-017-4325-2 PMID: 28578505
  4. ↑ Freer PE (2015) Mammographic breast density: impact on breast cancer risk and implications for screening. Radiographics 35 (2):302-15. DOI:10.1148/rg.352140106 PMID: 25763718
  5. ↑ Yue W, Wang JP, Li Y, Fan P, Liu G, Zhang N et al. (2010) Effects of estrogen on breast cancer development: Role of estrogen receptor independent mechanisms. Int J Cancer 127 (8):1748-57. DOI:10.1002/ijc.25207 PMID: 20104523
  6. ↑ Howell A, Evans GD (2011) Hormone replacement therapy and breast cancer. Recent Results Cancer Res 188 ():115-24. DOI:10.1007/978-3-642-10858-7_10 PMID: 21253794
  7. ↑ Ng AK, Travis LB (2009) Radiation therapy and breast cancer risk. J Natl Compr Canc Netw 7 (10):1121-8. PMID: 19930978
  8. ↑ Picon-Ruiz M, Morata-Tarifa C, Valle-Goffin JJ, Friedman ER, Slingerland JM (2017) Obesity and adverse breast cancer risk and outcome: Mechanistic insights and strategies for intervention. CA Cancer J Clin 67 (5):378-397. DOI:10.3322/caac.21405 PMID: 28763097
  9. ↑ McDonald JA, Goyal A, Terry MB (2013) Alcohol Intake and Breast Cancer Risk: Weighing the Overall Evidence. Curr Breast Cancer Rep 5 (3):. DOI:10.1007/s12609-013-0114-z PMID: 24265860
  10. ↑ 10.0 10.1 ACS (2005). "Breast Cancer Facts & Figures 2005-2006" (PDF). Retrieved 2007-04-26.
  11. ↑ Jansen-van der Weide MC, Greuter MJ, Jansen L, Oosterwijk JC, Pijnappel RM, de Bock GH (2010) Exposure to low-dose radiation and the risk of breast cancer among women with a familial or genetic predisposition: a meta-analysis. Eur Radiol 20 (11):2547-56. DOI:10.1007/s00330-010-1839-y PMID: 20582702
  12. ↑ Miglioretti DL, Lange J, van den Broek JJ, Lee CI, van Ravesteyn NT, Ritley D et al. (2016) Radiation-Induced Breast Cancer Incidence and Mortality From Digital Mammography Screening: A Modeling Study. Ann Intern Med 164 (4):205-14. DOI:10.7326/M15-1241 PMID: 26756460
  13. ↑ Ctv.Ca News Staff (2006-10-12). "Breast cancer more likely in farm workers: study". Ctv.Ca. Retrieved 2007-03-11.
  14. ↑ Danjou AM, Fervers B, Boutron-Ruault MC, Philip T, Clavel-Chapelon F, Dossus L (2015) Estimated dietary dioxin exposure and breast cancer risk among women from the French E3N prospective cohort. Breast Cancer Res 17 ():39. DOI:10.1186/s13058-015-0536-9 PMID: 25849111
  15. ↑ Warner M, Eskenazi B, Mocarelli P, Gerthoux PM, Samuels S, Needham L et al. (2002) Serum dioxin concentrations and breast cancer risk in the Seveso Women's Health Study. Environ Health Perspect 110 (7):625-8. DOI:10.1289/ehp.02110625 PMID: 12117637
  16. ↑ The Independent Avoid breast cancer. Sleep in the dark...

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