Breast cancer risk factors

One in eight women in Australia are estimated to develop breast cancer by the age of 85.

Generally it is not possible to determine what causes breast cancer in any individual woman. However, studies looking at very large numbers of women have shown there are some characteristics that are more common among groups of women who have developed breast cancer compared to groups of women who have not. These are called risk factors.

Having certain risk factors increases a woman’s chance of developing breast cancer.

Some of the risk factors for breast cancer include growing older, having a strong family history of the disease, being overweight, drinking alcohol and other lifestyle and environmental factors. Some of these factors are beyond your control but there are some things you can change.

However, having one or more risk factors for breast cancer does not mean you will get breast cancer. And many women who develop breast cancer have no obvious risk factors.

On the other hand there have been some factors that are thought to have a protective effect against breast cancer, like having children at a younger age and breastfeeding. However, women with protective factors may still develop breast cancer.

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below. The greater the number of stars, the higher the risk.

Please note not all risk factors for breast cancer have been included in this resource.

Personal characteristics

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below. The greater the number of stars, the higher the risk.

Gender Rating starRating starRating star
Being a woman is the main risk factor for breast cancer. Women are 100 times more likely to develop breast cancer than men.

The rest of this summary relates to breast cancer risk for women. More information about breast cancer in men is available here.

Age Rating starRating starRating star
Increasing age is one of the strongest risk factors for developing breast cancer.

Breast cancer can occur in younger women, but about three out of four breast cancer cases occur in women aged 50 years and older.

About one in 250 women in their 30s will develop breast cancer in the next ten years. This compares to about one in 30 for women in their 70s.

Estimated age-specific incidence rates for breast cancer, 2016

Estimated age-specific incidence rates for breast cancer, 2016

Source: Breast cancer in Australia [Internet]. Australian Institute of Health and Welfare. 2016. [cited 12 September 2016].  Available from: http://www.aihw.gov.au/cancer/breast/

Height Rating starEmpty rating starEmpty rating star
Being 175cm or taller is associated with a slightly increased risk for breast cancer.

Weight Rating starEmpty rating starEmpty rating star
Women who put on weight after menopause are at greater risk of developing breast cancer, and this risk increases with increasing body weight.

This is thought to be because fat tissue increases levels of the hormone oestrogen in the body – a known risk factor for breast cancer. Studies have shown that post-menopausal women who are overweight (with a BMI greater than 25) are at 21 to 43 per cent increased risk of breast cancer compared to leaner women (with a BMI less than 21).

Your BMI is calculated using your weight and height measurements. It can be used to determine if you are at a healthy weight, overweight, or obese. A BMI from 18.5 to 24.9 is considered a healthy weight range. A BMI between 25 and 29.9 is considered overweight, and a BMI of 30 or more is considered obese.*

Family history

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below. The greater the number of stars, the higher the risk.

Strong family history Rating starRating starEmpty rating star
The significance of a family history of breast cancer increases with:

  • the number of family members affected
  • the younger their ages at diagnosis
  • the closer the affected relatives are related to you.

The increase in risk is fairly small unless there are three or more first or second-degree relatives on the same side of the family with breast or ovarian cancer. It is important to note that a family history on your father’s side is just as important as it is on your mother’s side of the family.

The risk is stronger if two or more relatives have other characteristics associated with increased risk, such as being diagnosed before age 50 or being of Ashkenazi Jewish descent.

Although women who have one or more first-degree relatives with a history of breast cancer are at increased risk, most will never develop breast cancer. Of those women with a family history who do develop breast cancer, most will be older than 50 years when their cancer is diagnosed.

Despite the importance of family history as a risk factor, eight out of nine women who develop breast cancer do not have an affected mother, sister, or daughter.

Inherited genetic factors Rating starRating starRating star
Breast or ovarian cancer caused by inheriting a faulty gene is called hereditary cancer. We all inherit a set of genes from each of our parents. Sometimes there is a fault in one copy of a gene which stops that gene working properly. This fault is called a mutation.

There are several gene mutations that may be involved in the development of breast or ovarian cancer. The most common mutations are in the BRCA1 and BRCA2 genes. These are genes that normally prevent a woman developing breast or ovarian cancer. However, mutations in these genes increase a woman’s risk of developing breast cancer.

Ashkenazi is the term used to refer to Jews who have ancestors from Eastern or Central Europe, such as Germany, Poland, Hungary, Lithuania, Ukraine or Russia. As Ashkenazi Jews descend from a small population group, they have more genes in common than the general population.

While people of Ashkenazi Jewish descent don’t have any more faulty genes than anyone else, they do have a high prevalence of some gene faults and very low levels of others. Three gene faults associated with increased risk of breast and ovarian cancer have been found to be one of the genetic traits which are more common amongst Ashkenazi Jews than the general population. These gene faults occur in two per cent of Ashkenazi Jews compared to 0.2 per cent of the general population.

For more information about family history of breast cancer, visit canceraustralia.gov.au

Factors relating to the breast itself

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below.  The greater the number of stars, the higher the risk.

A previous breast condition Rating starRating starRating star
Being previously diagnosed with a non-invasive breast condition such as ductal carcinoma in situ (DCIS)or lobular carcinoma in situ (LCIS), is associated with an increased risk of developing invasive breast cancer.

Breast density Rating starEmpty rating starEmpty rating star
Increased breast density is associated with an increased risk of breast cancer.1,2

Your breast density is something that can only be seen on a mammogram. A mammogram of a woman with dense breasts will appear much like white cotton wool. A mammogram of a woman with less dense breasts will appear more grey and transparent. Breast density cannot be measured by physical breast examination.

At this time, there is no consensus about the most effective way to manage breast density.3

Research to better quantify breast density and identify the reasons why women of the same age differ so much in breast density, may lead to a better understanding of breast density as a risk factor for breast cancer.

References

  1. McCormack, V.A. and I. dos Santos Silva. (2006) ‘Breast density and parenchymal patterns as markers of breast cancer risk: a meta-analysis.’ Cancer Epidemiol Biomarkers Prev, 15(6): 1159-69.
  2. Pettersson, A., et al. (2014). ‘Mammographic density phenotypes and risk of breast cancer: a meta-analysis.’ Journal of the National Cancer Institute, 106(5): dju078
  3. Ng, K-H and Lau, S. (2015). ‘Vision 20/20: Mammographic breast density and its clinical applications.’ Med Phys 42(12):7059-7077. doi: 0094-2405/2015/42(12)/7059/19
Hormones and menstrual history

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below. The greater the number of stars, the higher the risk.

Naturally occurring hormones (endogenous) Rating starEmpty rating starEmpty rating star
If you are post-menopausal, having increased concentrations of naturally occurring oestrogens or androgens is associated with higher breast cancer risk.

If you are pre-menopausal, having high levels of a hormone called ‘insulin-like growth factor’ is associated with a small increase in risk of breast cancer.

Consumed hormones (exogenous) Rating starEmpty rating starEmpty rating star
A small increase in risk exists while you are taking the oral contraceptive pill and in the ten years after stopping it. However, the underlying risk of breast cancer is low at the young ages when women typically use the pill.

If you are post-menopausal, taking combined hormone replacement therapy (HRT) for five or more years is associated with an increased risk of breast cancer. This risk is not evident for oestrogen-only forms of HRT. Click here to view Cancer Australia's position statement and recommendations on HRT and breast cancer risk.

Age at menopause Rating starEmpty rating starEmpty rating star
Women who experience menopause later (at age 55 or after) have twice the risk of developing breast cancer of women who experience natural menopause at ages younger than 45.

Age at puberty Rating starEmpty rating starEmpty rating star
Reaching puberty early prolongs the amount of time you are exposed to the fluctuating levels of oestrogen and other female hormones that are associated with the menstrual cycle. Starting menstruation before the age of 12 is associated with higher breast cancer risk.

Exposure to diethylstilbestrol (DES) Rating starEmpty rating starEmpty rating star
For more information on DES.

Lifestyle & health

A three-star rating system has been used to give you an indication of the level of breast cancer risk associated with the factors below. The greater the number of stars, the higher the risk.

Affluence Rating starEmpty rating starEmpty rating star
Breast cancer occurs more frequently in women who live in more affluent areas. This probably relates to lifestyle factors.

Alcohol consumption Rating starEmpty rating starEmpty rating star
Drinking more than two glasses of alcohol each day is associated with an increased risk of breast cancer. This includes beer, wine and spirits. Your risk increases with each additional 10g of alcohol intake per day.

Hodgkin disease Rating starRating starRating star
Breast cancer occurs more frequently in women who have previously been diagnosed with Hodgkin disease. The risk of breast cancer is greatest for women diagnosed with Hodgkin disease when they were younger than 30 years of age. The increased risk of breast cancer is generally considered to be a consequence of treatment with radiation and/or chemotherapy for Hodgkin disease. When breast cancer does occur in women previously treated for Hodgkin disease, women are more likely to be diagnosed at a younger age.

The increased risk of breast cancer associated with Hodgkin disease appears to be lower for women receiving newer forms of treatment.

Exposure to high levels of ionising radiation Rating starEmpty rating starEmpty rating star
High dose ionising radiation, as is experienced with some cancer treatments and in certain environments, is associated with increased breast cancer risk. The highest risks are associated with an earlier age of exposure.

Exposure to tobacco smoke Rating starEmpty rating starEmpty rating star
Recent research raises the possibility that environmental tobacco smoke or passive smoking may increase the risk of breast cancer in some subgroups of women.

Protective Factors

A three-star rating system has been used to give you an indication of the level of protection from breast cancer associated with the factors below. The greater the number of stars, the stronger the protective factor.

Regular physical activity Rating starEmpty rating starEmpty rating star
Active women of all ages are at reduced risk of breast cancer compared to women who do not exercise.

The exact amount of physical activity needed to reduce your risk is not yet clear. However, studies have shown that one and a half to four hours per week of brisk walking (or equivalent) reduces the risk of breast cancer in post-menopausal women. And the more exercise you do, the bigger the benefits in lowering your risk.

Child-bearing Rating starRating starRating star
Having children is associated with a decreased risk of breast cancer. The more children women have, the more their risk of breast cancer appears to be reduced.

Among women who have had children, having them at a younger age (less than 30 years) is associated with lower breast cancer risk.

Breast feeding Rating starEmpty rating starEmpty rating star
Breastfeeding for a total of 12 months or longer can slightly reduce your breast cancer risk.

Unproven risk factors

Research has shown there is no link between termination of pregnancy and increased risk of breast cancer. This includes both induced abortion and spontaneous miscarriage.

Several studies have found that silicone breast implants do not increase a woman’s risk of developing breast cancer.

Research does not support the claim that underwire or tight-fitting bras increase a woman’s risk of breast cancer.

There has not been enough research to determine whether anti-perspirant deodorant is associated with an increased risk of breast cancer. Further studies are needed.

The majority of research to date does not show a link between stress and increased risk of breast cancer. However, there have been some conflicting results. More research is needed in this area.

Research has shown a bump or knock to the breast does not cause breast cancer. However, it can draw attention to an existing lump in the breast.

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