Am I at Risk for Breast Cancer?

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  • All women are at some risk for breast cancer, but only a small number will develop it (1 in 9 Canadian women during their lifetime). (1)
  • As we age, our risk increases. (2) 
  • Most women who develop breast cancer do not have any family history of the disease. (3)
  • Only 1 - 2 % of women are at high risk for breast cancer. (4)

A risk factor is something that increases a person’s chance for developing a disease. Breast cancer is a complex disease and it is often impossible to predict or know its exact cause. Breast cancer usually results from the interplay between a variety of genetic and environmental factors and often the cause is unknown.

Risk factors

Women’s breasts contain two main types of tissue: fatty tissue (made of fat) and glandular tissue (made up of ducts and glands that produce milk).
 
Breast density describes the amount of glandular tissue in the breasts. Younger women often have denser breasts than older women. As women age, their breasts often become more fatty and less dense.
 
Women with dense breasts may have an increased risk of developing breast cancer, compared to those who don’t. Breast density may be inherited. Breast density can only be assessed by having a mammogram. Women who have multiple family members with dense breasts may want to speak with a health care provider about having a mammogram to assess breast density.
 
Increased breast density may also make mammograms more difficult to read as both tumors and dense breast tissue appear white, making it difficult to determine if a tumour is present. (5)
 
When you have a mammogram your report will include your breast density. 
Some screening programs may recommend yearly mammograms if your breasts have a density of 75% or more.

Women who have taken combination hormone therapy (also often called ‘hormone replacement therapy’ or HRT) for long periods (5 years or longer) are at an increased risk of developing breast cancer. (6) (7)

Women who take oral contraceptives, birth control pills that contain estrogen and progestogen, are at a slightly increased risk of developing breast cancer, compared to women who do not take them. This increased risk disappears ten years after stopping the pill but current and recent (within the past 10 years) users remain at a slightly increased risk. (8)

Alcohol is a known carcinogen – that is, a substance that causes cancer. A woman’s risk for breast cancer increases with the amount of alcohol consumed. Women who drink more than one drink per day may be at increased risk for breast cancer.(9) (10) (11)

Evidence also suggests that weight gain during adulthood increases the risk of breast cancer in post-menopausal women. (12) (13)

In addition, women who are taller have a slightly higher risk of developing breast cancer, likely due to hormonal factors, diet and energy input early in life. (13)

About 5 to 10% of all breast cancer cases are hereditary (14), meaning there is a genetic component or predisposition to breast cancer in the family. Any of the following family history or gene changes might suggest an increased risk of developing breast cancer:

  • You have been assessed at a genetics clinic and have:
    • A known gene mutation (e.g., BRCA1, BRCA2, e-cadherin) or another syndrome (e.g., Li-Fraumeni, Cowden or Bannayan-Riley-Ruvalcabe syndromes);   or 
    • A higher lifetime risk for breast cancer, based on a validated breast cancer risk assessment questionnaire.
  • You have a first degree family member (parent, sibling or child) that has tested positive for a gene mutation (e.g., BRCA1, BRCA2)
  • You have a family history of breast cancer in two or more first degree relatives (parent, sibling or child)

Other factors that might put you at higher risk include:

  • You have two or more first degree relatives (parent, sibling or child) diagnosed with ovarian cancer,  or
  • You are of Ashkenazi Jewish heritage (Jewish heritage of Eastern European descent) and have two or more first degree relatives (parent, sibling or child) with breast or ovarian cancer

What does it mean to have a BRCA gene mutation?

Everyone has BRCA1 (BReast CAncer 1) and BRCA2 (BReast CAncer 2) genes. They play a role in repairing damage to our DNA to keep cells growing and dividing normally. A gene mutation occurs when a change is made to the gene that prevents it from functioning properly. Gene mutations can occur spontaneously (at random) or in some families, they can be inherited (passed down from parent to child).  Researchers have discovered several genes that are linked to an increased risk of breast cancer when they have mutations. The most common of these genes are the BRCA1 and BRCA2 genes.

Carrying a BRCA1 or BRCA2 gene mutation increases the risk of developing breast or ovarian cancer, as well as certain other cancers. 

Having a BRCA1 or BRCA2 gene mutation, however, does not mean you will develop cancer, only that you are at increased risk to develop cancer. 

At this time, no one can predict:

  • your exact risk for developing cancer
  • the type of cancer you may develop
  • the age that a cancer develops

In women, having a BRCA1 or BRCA2 gene mutation:

  1. increases your risk of developing breast cancer over your lifetime
  2. increases the chance of developing cancer earlier in life
  3. increases the risk of developing a second (unrelated) breast cancer in the same or opposite breast, if you have had a prior diagnosis of breast cancer
  4. increases the risk of developing an aggressive form of breast cancer known as triple negative breast cancer

In men, having a BRCA gene mutation:

  1. increases your risk of developing breast cancer over your lifetime
  2. increases the chance of developing other cancers, such as prostate cancer

For more information about genetic risk, including an overview of genetics, and to learn more about how to manage risk factors, please visit CBCF’s web pages on hereditary breast cancer: www.mygenes.org 

If you are concerned about being at high risk for breast cancer, speak with your healthcare provider.

 


References:
(1)

Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics 2015. Toronto, ON: Canadian Cancer Society; 2015.

(2)

The Canadian Task Force on Preventive Health Care. Recommendations on screening for breast cancer in average-risk women aged 40–74 years. CMAJ Can Med Assoc J. 2011 Nov 22;183(17):1991–2001. 

(3)

Beral V, Bull D, Doll R, Peto R, Reeves G. Familial breast cancer: Collaborative reanalysis of individual data from 52 epidemiological studies including 58 209 women with breast cancer and 101 986 women without the disease. Lancet 2001;358(9291):1389-1399.

(4)

Evans DGR, Warwick J, Astley SM, Stavrinos P, Sahin S, Ingham S, et al. Assessing individual breast cancer risk within the U.K. National Health Service Breast Screening Program: A new paradigm for cancer prevention. Cancer Prev Res 2012;5(7):943-951.

(5)

Boyd NF, Guo H, Martin LJ, Sun L, Stone J, Fishell E, et al. Mammographic density and the risk and detection of breast cancer. New Engl J Med 2007;356(3):227-236.

(6)

Chlebowski RT, Hendrix SL, Langer RD, Stefanick ML, Gass M, Lane D, et al. Influence of Estrogen Plus Progestin on Breast Cancer and Mammography in Healthy Postmenopausal Women: The Women's Health Initiative Randomized Trial. J Am Med Assoc 2003;289(24):3243-3253.

(7)

Stefanick ML, Anderson GL, Margolis KL, Hendrix SL, Rodabough RJ, Paskett ED, et al. Effects of conjugated equine estrogens on breast cancer and mammography screening in postmenopausal women with hysterectomy. J Am Med Assoc 2006;295(14):1647-1657.

(8)

International Agency for Research on Cancer (IARC). Volume 91: Combined estrogen-progestogen contraceptives and combined estrogen-progestogen menopausal therapy. Lyon: International Agency for Research on Cancer; 2007. Retrieved from: http://monographs.iarc.fr/ENG/Monographs/vol91/mono91.pdf.

(9)

Allen NE, Beral V, Casabonne D, Kan SW, Reeves GK, Brown A, et al. Moderate alcohol intake and cancer incidence in women. J Natl Cancer Inst 2009;101(5):296-305.

(10)

Boyle P, Boffetta P. Alcohol consumption and breast cancer risk. Breast Cancer Res 2009;11(SUPPL. 3).

(11)

Cao Y, Willett WC, Rimm EB, Stampfer MJ, Giovannucci EL. Light to moderate intake of alcohol, drinking patterns, and risk of cancer: Results from two prospective US cohort studies. BMJ (Online) 2015;351.

(12)

Keum N, Greenwood DC, Lee DH, Kim R, Aune D, Ju W, et al. Adult weight gain and adiposity-related cancers: a dose-response meta-analysis of prospective observational studies. J Natl Cancer Inst 2015;107(3).

(13)

World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project  Report. Food, Nutrition, Physical Activity, and the Prevention of Breast Cancer; 2010.

(14)

National Cancer Institute. (2013, December 16). Genetics of Breast and Ovarian Cancer (PDQ®) Health Professional Version. Bethesda, MD: National Cancer Institute.