Breast cancer

Risk factors for breast cancer

Some of the risk factors for breast cancer are listed below.

Source:
Dixon M.
ABC of breast diseases.
BMJ Publishing Group, London, UK; 2001.

¹ When you read this list, please remember that just because you have one or more of these risk factors, it doesn't mean you will definitely get breast cancer.

Your age when you have your first baby can affect your risk of breast cancer.

Risk factors you can't change

Being older: This is the strongest risk factor. The risk of breast cancer increases with age. It doubles every decade until you reach

menopause
When a woman stops having periods, it is called menopause. This usually happens around the age of 50.

menopause. To get an idea of your chance of getting cancer in the next 10 years, see How common is breast cancer?
Starting periods early (before 11) and going through menopause late (after 54): These both increase the risk of breast cancer, perhaps because some breast cancers are encouraged to grow by

hormones
Hormones are chemicals that are made in certain parts of the body. They travel through the bloodstream and have an effect on other parts of the body. For example, the female sex hormone estrogen is made in a woman's ovaries. Estrogen has many different effects on a woman's body. It makes the breasts grow at puberty and helps control periods. It is also needed to get pregnant.

hormones. If you start your periods early and go through menopause late, then the female hormone

estrogen
Estrogen is the name given to three female sex hormones: oestradiol, oestrone and oestriol. Estrogen causes women's sexual development during puberty: it is needed to develop breasts, have periods and get pregnant. Estrogen is also thought to affect women's health in other ways. It may influence their mood, cholesterol levels and how their bones grow. Men have very low levels of estrogen in their bodies, but doctors aren't completely sure what it does. Estrogen is an important ingredient in most types of contraceptive pill and hormone replacement therapy.

estrogen will be around in your body for longer.

Source:
National Cancer Institute.
Breast cancer (PDQ): prevention (health professional version).
Available at http://www.nci.nih.gov (accessed on 7 May 2009).

²

Source:
Brinton LA, Schairer C, Hoover RN, et al.
Menstrual factors and risk of breast cancer.
Cancer Investigation. 1988; 6: 245-254.

³
Genes: Most breast cancers happen by chance. But about 5 percent to 10 percent of the women who get breast cancer do so because they've inherited an abnormal

genes
Your genes are the parts of your cells that contain instructions for how your body works. Genes are housed on chromosomes, structures that sit in the nucleus at the middle of each of your cells. You have 23 pairs of chromosomes in your normal cells, each of which has thousands of genes. You get one set of chromosomes, and all of the genes that are on them, from each of your parents.

gene.

Source:
McPherson K, Steel CM, Dixon JM.
Breast cancer: epidemiology, risk factors and genetics.
BMJ. 2000; 321: 624-680.

⁴ Several genes can increase the risk of breast cancer if they are faulty. The ones that doctors can test for are called BRCA1 and BRCA2.

Source:
Miki Y, Swensen J, Shattuck-Eidens D, et al.
A strong candidate for the breast and ovarian cancer susceptibility gene BRCA1.
Science. 1994; 266: 66-71.

⁵

Source:
Wooster R, Neuhausen SL, Mangion J, et al.
Localization of a breast cancer susceptibility gene, BRCA2, to chromosome 13q12-13.
Science. 1994; 265: 2088-2090.

⁶ If you have a fault on one of these genes, you have a higher risk of getting breast cancer. But you still might not get breast cancer. Women with a faulty BRCA1 or BRCA2 gene have a 56 percent to 85 percent chance of getting breast cancer.

Source:
Easton DF, Ford D, Bishop DT.
Breast and ovarian cancer incidence in BRCA1-mutation carriers.
American Journal of Human Genetics. 1995; 56: 265-271.

⁷

Source:
Struewing JP, Hartge P, Wacholder S, et al.
The risk of cancer associated with specific mutations of BRCA1 and BRCA2 among Ashkenazi Jews.
New England Journal of Medicine. 1997; 336: 1407-1408.

⁸ Having an abnormal BRCA2 gene increases the risk of breast cancer in both men and women.
Family history: Your risk of getting breast cancer may be higher if your mother or sister got it before age 50. Your risk is also higher if you have relatives with both breast cancer and ovarian cancer.
You've had breast cancer before: If you've had cancer in one breast, you have an increased risk of getting a new cancer in the other breast or in another part of the same breast. However, you'll have regular checks to make sure that any new cancer is picked up early. Some women take tamoxifen to reduce the risk of their cancer coming back. This can also lower your chance of getting a new cancer.

Source:
American Cancer Society.
Detailed guide: breast cancer. What are the risk factors for breast cancer?
Available at http://www.cancer.org (accessed on 7 May 2009).

⁹ To read more, see Tamoxifen for early breast cancer.
You've had radiation therapy: Your risk of getting breast cancer is increased if you had

radiation therapy
This treatment uses high-energy X-rays to kill cancer cells. It's most often used for tumors that are hard to treat with surgery alone. You won't feel any pain during this treatment, but you may get some side effects afterward.

radiation therapy to your chest as a child or young adult. You might have had radiation to treat another cancer such as Hodgkin's disease or non-Hodgkin's lymphoma.

Source:
John EM, Kelsey JL.
Radiation and other environmental exposures and breast cancer.
Epidemiologic Reviews. 1993; 15: 157-162.

¹⁰

Source:
Bhatia S, Robison LL, Oberlin O, et al.
Breast cancer and other second neoplasms after childhood Hodgkin's disease.
New England Journal of Medicine. 1996; 334: 745-751.

¹¹

Other risk factors

You may be able to influence some of these factors.

Being older than 35 when your first child is born: It's not clear why this should increase a woman's risk of breast cancer. Women who never have children also seem to have an increased risk. In one study, women who had a baby before they were 20 were half as likely to get breast cancer as women who hadn't been pregnant or who had a baby at 35 or older.

Source:
Henderson BE, Pike MC, Ross RK, et al.
Epidemiology and risk factors.
In: Bonadonna G (editor). Breast cancer: diagnosis and management. Wiley, Chichester, UK; 1984.

¹²
Breast-feeding: Breast-feeding reduces the risk of breast cancer. The longer you breast-feed, the greater the protection.

Source:
Furberg H, Newman B, Moorman P, et al.
Lactation and breast cancer risk.
International Journal of Epidemiology. 1999; 28: 396-402.

¹³

Source:
Collaborative Group on Hormonal Factors in Breast Cancer.
Breast cancer and breast feeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries including 50302 women with breast cancer and 96973 women without disease.
Lancet. 2002; 360: 187-195.

¹⁴
Hormone replacement therapy (HRT): Taking HRT increases your risk of breast cancer.

Source:
National Cancer Institute.
Breast cancer (PDQ): prevention (health professional version).
Available at http://www.nci.nih.gov (accessed on 7 May 2009).

² It makes breast tissue denser, and this makes it harder to read a

mammogram
A mammogram is a special kind of X-ray picture of the breast.

mammogram and diagnose breast cancer from it. To read more, see HRT in our section on menopause.
Birth control pills: Some researchers have found that while you are taking birth control pills, your risk of getting breast cancer increases by a small amount. But once you stop taking them, this extra risk seems to go away over the next 10 years. Other researchers have found that taking birth control pills don't seem to increase the risk of breast cancer.

Source:
Marchbanks PA, McDonald JA, Wilson HG, et al.
Oral contraceptives and the risk of breast cancer.
New England Journal of Medicine. 2002; 346: 2025-2032.

¹⁵

Source:
Collaborative Group on Hormonal Factors in Breast Cancer.
Breast cancer and hormonal contraceptives: further results.
Contraception. 1996: 54 (supplement): S1-S106.

¹⁶
Obesity: After menopause, being obese seems to increase a woman's chance of getting breast cancer if she hasn't taken HRT (see above). This could be because fat helps your body make estrogen, and this seems to encourage some breast cancers to grow. Being obese after menopause can double your risk of breast cancer.

Source:
Morimoto LM, White E, Chen Z, et al.
Obesity, body size, and risk of post menopausal breast cancer: the Women's Health Initiative (United States).
Cancer Causes Control. 2002; 12: 741-751.

¹⁷ A good way to find out whether you are obese is to figure out your body mass index (BMI). This measurement looks at your weight in relation to your height. Many medical organizations say that a BMI of 25 to 29.9 means you're overweight, and a BMI of 30 or more means you're obese. You can use our calculator to figure out your own BMI.
The food you eat: In groups of people who eat a high-fat diet, women are more likely to die of breast cancer.

Source:
National Cancer Institute.
Breast cancer (PDQ): prevention (health professional version).
Available at http://www.nci.nih.gov (accessed on 7 May 2009).

²

Source:
Smith-Warner SA, Spiegelman D, Yaun SS, et al.
Intake of fruits and vegetables and risk of breast cancer: a pooled analysis of cohort studies.
Journal of the American Medical Association. 2001; 285: 769-776.

¹⁸ But there hasn't been enough research to be sure about this.

Source:
Hunter DJ, Spiegelman D, Adami HO, et al.
Cohort studies of fat intake and the risk of breast cancer: a pooled analysis.
New England Journal of Medicine. 1996; 224: 356-361.

¹⁹ In a recent study, eating a low-fat diet did not reduce the risk of breast cancer among women who had been through menopause.

Source:
Prentice RL, Caan B, Chlebowski RT, et al.
Low-fat dietary pattern and risk of invasive breast cancer.
Journal of the American Medical Association. 2006; 295: 629-642.

²⁰
Alcohol: Drinking alcohol slightly increases your risk of breast cancer. One review of 53 studies found that women who have three or four drinks a day increase their risk by about a third. The more you drink, the greater your risk.

Source:
Hamajima N, Hirose K, Tajima K, et al.
Alcohol, tobacco and breast cancer: collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 women without the disease.
British Journal of Cancer. 2002; 87: 1234-1245.

²¹ The effects of alcohol on your risk of breast cancer may be increased if you're also taking HRT (see above).

Source:
Chen WY, Colditz GA, Rosner B, et al.
Use of post menopausal hormones, alcohol and risk for invasive breast cancer.
Annals of Internal Medicine. 2002; 137: 798-804.

²² However, your overall risk of breast cancer may still be small even if you drink a lot. Some of the other things we mention on this page have a much bigger impact on your risk.
Exercise: Lack of exercise may increase your risk of breast cancer.

Source:
Bernstein L, Henderson BE, Hanisch R, et al.
Physical exercise and reduced risk of breast cancer in young women.
Journal of the National Cancer Institute. 1994; 86: 1403-1408.

²³

Source:
Friedenreich CM.
Physical activity and cancer prevention: from observational to intervention research.
Cancer Epidemiology Biomarkers and Prevention. 2001; 10: 287-301.

²⁴

Source:
Thune I, Brenn T, Lund E, et al.
Physical activity and the risk of breast cancer.
New England Journal of Medicine. 1997; 336: 1269-1275.

²⁵ But the research on this is mixed.

Source:
National Cancer Institute.
Breast cancer (PDQ): prevention (health professional version).
Available at http://www.nci.nih.gov (accessed on 7 May 2009).

² In one study, walking briskly for as little as one-and-a-quarter hours to two-and-a-half hours each week reduced a woman's risk of breast cancer by 18 percent. Walking 10 hours a week reduced the risk a little more.

Source:
National Cancer Institute.
Breast cancer (PDQ): prevention (health professional version).
Available at http://www.nci.nih.gov (accessed on 7 May 2009).

²
Smoking: It's not clear if there's a link between smoking and breast cancer. In the past, studies suggested that women who smoked were less likely to get breast cancer than those who didn't. But recent research suggests that it might increase the risk of breast cancer for women who start smoking in early adolescence and smoke for many years.

Source:
Terry PD, Miller AB, Rohan TE.
Cigarette smoking and breast cancer risk: a long latency period?
International Journal of Cancer. 2002; 100: 723-728.

²⁶

Source:
Reynolds P, Hurley S, Goldberg DE, et al.
Active smoking, household passive smoking, and breast cancer: evidence from the California Teachers Study.
Journal of the National Cancer Institute. 2004; 96:29-37.

²⁷ Being regularly exposed to second-hand smoke may also increase a woman's risk.

Source:
Miller MD, Marty MA, Broadwin R, et al.
The association between exposure to environmental tobacco smoke and breast cancer: a review by the California Environmental Protection Agency.
Preventative Medicine. 2007; 44: 93-106.

²⁸

Sources for the information on this page:

Dixon M.ABC of breast diseases.BMJ Publishing Group, London, UK; 2001.

National Cancer Institute.Breast cancer (PDQ): prevention (health professional version).Available at http://www.nci.nih.gov (accessed on 7 May 2009).

Brinton LA, Schairer C, Hoover RN, et al.Menstrual factors and risk of breast cancer.Cancer Investigation. 1988; 6: 245-254.

McPherson K, Steel CM, Dixon JM.Breast cancer: epidemiology, risk factors and genetics.BMJ. 2000; 321: 624-680.

Miki Y, Swensen J, Shattuck-Eidens D, et al.A strong candidate for the breast and ovarian cancer susceptibility gene BRCA1.Science. 1994; 266: 66-71.

Wooster R, Neuhausen SL, Mangion J, et al.Localization of a breast cancer susceptibility gene, BRCA2, to chromosome 13q12-13.Science. 1994; 265: 2088-2090.

Easton DF, Ford D, Bishop DT.Breast and ovarian cancer incidence in BRCA1-mutation carriers.American Journal of Human Genetics. 1995; 56: 265-271.

Struewing JP, Hartge P, Wacholder S, et al.The risk of cancer associated with specific mutations of BRCA1 and BRCA2 among Ashkenazi Jews.New England Journal of Medicine. 1997; 336: 1407-1408.

American Cancer Society.Detailed guide: breast cancer. What are the risk factors for breast cancer?Available at http://www.cancer.org (accessed on 7 May 2009).

John EM, Kelsey JL.Radiation and other environmental exposures and breast cancer.Epidemiologic Reviews. 1993; 15: 157-162.

Bhatia S, Robison LL, Oberlin O, et al.Breast cancer and other second neoplasms after childhood Hodgkin's disease.New England Journal of Medicine. 1996; 334: 745-751.

Henderson BE, Pike MC, Ross RK, et al.Epidemiology and risk factors.In: Bonadonna G (editor). Breast cancer: diagnosis and management. Wiley, Chichester, UK; 1984.

Furberg H, Newman B, Moorman P, et al.Lactation and breast cancer risk.International Journal of Epidemiology. 1999; 28: 396-402.

Collaborative Group on Hormonal Factors in Breast Cancer.Breast cancer and breast feeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries including 50302 women with breast cancer and 96973 women without disease.Lancet. 2002; 360: 187-195.

Marchbanks PA, McDonald JA, Wilson HG, et al.Oral contraceptives and the risk of breast cancer.New England Journal of Medicine. 2002; 346: 2025-2032.

Collaborative Group on Hormonal Factors in Breast Cancer.Breast cancer and hormonal contraceptives: further results.Contraception. 1996: 54 (supplement): S1-S106.

Morimoto LM, White E, Chen Z, et al.Obesity, body size, and risk of post menopausal breast cancer: the Women's Health Initiative (United States).Cancer Causes Control. 2002; 12: 741-751.

Smith-Warner SA, Spiegelman D, Yaun SS, et al.Intake of fruits and vegetables and risk of breast cancer: a pooled analysis of cohort studies.Journal of the American Medical Association. 2001; 285: 769-776.

Hunter DJ, Spiegelman D, Adami HO, et al.Cohort studies of fat intake and the risk of breast cancer: a pooled analysis.New England Journal of Medicine. 1996; 224: 356-361.

Prentice RL, Caan B, Chlebowski RT, et al.Low-fat dietary pattern and risk of invasive breast cancer.Journal of the American Medical Association. 2006; 295: 629-642.

Hamajima N, Hirose K, Tajima K, et al.Alcohol, tobacco and breast cancer: collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 women without the disease.British Journal of Cancer. 2002; 87: 1234-1245.

Chen WY, Colditz GA, Rosner B, et al.Use of post menopausal hormones, alcohol and risk for invasive breast cancer.Annals of Internal Medicine. 2002; 137: 798-804.

Bernstein L, Henderson BE, Hanisch R, et al.Physical exercise and reduced risk of breast cancer in young women.Journal of the National Cancer Institute. 1994; 86: 1403-1408.

Friedenreich CM.Physical activity and cancer prevention: from observational to intervention research.Cancer Epidemiology Biomarkers and Prevention. 2001; 10: 287-301.

Thune I, Brenn T, Lund E, et al.Physical activity and the risk of breast cancer.New England Journal of Medicine. 1997; 336: 1269-1275.

Terry PD, Miller AB, Rohan TE.Cigarette smoking and breast cancer risk: a long latency period?International Journal of Cancer. 2002; 100: 723-728.

Reynolds P, Hurley S, Goldberg DE, et al.Active smoking, household passive smoking, and breast cancer: evidence from the California Teachers Study.Journal of the National Cancer Institute. 2004; 96:29-37.

Miller MD, Marty MA, Broadwin R, et al.The association between exposure to environmental tobacco smoke and breast cancer: a review by the California Environmental Protection Agency.Preventative Medicine. 2007; 44: 93-106.

This information was last updated on May 11, 2009

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