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Risk factors

Research has shown that some things can increase your chance of getting breast cancer. These are called 'risk factors'. However, as we are all different, risk factors will not affect us all in the same way. One person may have many risk factors and not develop breast cancer, while another may have very few and be diagnosed with it.

You can use Cancer Australia’s risk calculator to help give you an understanding of your level of risk for developing breast cancer compared to another woman of your age group. The questions in this calculator are based on the most important risk factors for breast cancer according to Cancer Australia’s up-to-date review of international evidence.

Main risk factors

The main risk factors for breast cancer are the ones you can’t change:

  • being a woman
  • getting older
  • having a strong family history of breast cancer
  • inheriting a faulty gene that increases the risk

Being a woman

Being a woman is the single biggest risk factor for developing breast cancer. One in eight Australian women will develop breast cancer in their lifetime.

In 2015, 15,600 are expected to be diagnosed with breast cancer. This is an average of 42 women every day.

Breast cancer can also affect men. Around 145 men are diagnosed in Australia each year.

Age

As with many other diseases, your risk of breast cancer increase as you get older. Although breast cancer occurs in younger women, the majority of breast cancers occur after menopause. About 3 out of 4 of breast cancer cases occur in women 50 years and over.

Family history

You may be surprised to know that 90-95% of all breast cancers have nothing to do with family history. However, having one or more first-degree relatives or second-degree relatives on the same side of the family with breast cancer increases your risk.

Genetics

Around 5-10% of breast cancers occur in women whose families have a gene mutation that is passed down through the family and puts them at greater risk of developing breast cancer.

The BRCA1 and BRCA2 gene mutations are two mutations known to be associated with hereditary breast cancer. Women who carry these mutations can also be at increased risk of developing ovarian cancer.

BRCA mutations are more common in Jewish people of Ashkenazi (Eastern Europe) origin than in other racial and ethnic groups, but they can occur in any family.

It is suspected there are other gene mutations that have not yet been identified but that may increase your risk of developing breast cancer.

If you have a strong family history of breast cancer - that is two or more first-degree (mother, sister, daughter) or second-degree (grandmother, aunt, niece) relatives on the same side of the family who have been diagnosed with breast cancer - there is a chance your family may carry a breast cancer gene mutation.

While breast cancer is considered a woman's disease, it can affect men and the BRCA1 and BRCA2 mutations can be passed through your father's side of the family as well as your mother's.

If you carry one of the BRCA gene mutations, or have a strong family history of breast cancer, you are at higher risk of developing breast cancer than people in the general population. However, this does not mean you will get breast cancer. It means that your risk is greater than that of the general population.

If you are concerned about the risk of breast cancer in your family, you may want to talk to your doctor or contact a Family Cancer Clinic. See our page breast cancer in the family for further information and advice.

Other risk factors

There are other known risk factors for breast cancer which are listed below. The good news is that you can change most of these by making healthy lifestyle choices. For some advice on doing this, talk to your doctor and visit our reducing your risk page.

Being overweight or obese

Overweight and obese women have a higher risk of being diagnosed with breast cancer compared to women who maintain a healthy weight, especially after menopause. Being overweight also can increase the risk of the breast cancer coming back (recurrence) in women who have had the disease.

Fat tissue is the body’s main source of oestrogen after menopause, when the ovaries stop producing it. Having more fat tissue means having higher oestrogen levels, which may increase breast cancer risk.

Drinking alcohol

Studies, including a UK study of more than 28,000 women, have shown that drinking alcohol increases your risk of developing breast cancer. Alcohol can limit your liver’s ability to control the levels of oestrogen in your blood, which can increase your risk. It may also increase your risk by damaging DNA in cells.

Smoking

Although there is still no clear link between smoking and breast cancer, toxins from cigarettes have been found in breast cells. As smoking is a major cause of heart disease, lung cancer and many other cancers, not smoking is always a smart health choice. If you smoke and drink, your risk for some cancers increases even more. This is because tobacco and alcohol work together to damage the cells of the body.

Smoking also can increase complications from breast cancer treatment, including:

  • damage to the lungs from radiation therapy
  • difficulty healing wounds after surgery and breast reconstruction
  • higher risk of blood clots when taking hormone therapy medicines

Personal history of early breast cancer

Women diagnosed with invasive (early) breast cancer are at a higher risk of developing cancer in their other breast.

There are also a number of non-invasive breast conditions that are associated with an increased risk of breast cancer. These include ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS) and atypical ductal hyperplasia (a type of benign breast condition).

DCIS

Ductal carcinoma in situ (DCIS) is the most common type of non-invasive breast cancer. It starts in the milk ducts and is non-invasive because it hasn't spread into any surrounding breast tissue. DCIS isn't life-threatening, but having DCIS increases your risk of developing invasive (early) breast cancer. You can find out more on our page on DCIS.

Results from a recent Australian study found that between 1995 and 2005, 13,749 women were diagnosed with DCIS and that, by the end of 2005, 706 (5%) of those women had developed invasive breast cancer even though they had received treatment for DCIS.

Essentially this study found that women who have been diagnosed with DCIS are, on average, 3.9 times more likely to develop invasive breast cancer than Australian women of a similar age who have not had DCIS.

However, it is important to recognise that not every woman with DCIS will develop invasive breast cancer.

LCIS

Lobular carcinoma in situ (LCIS) is a non-invasive breast cancer that grows in the lobules (the milk-producing glands at the end of breast ducts). It is non-invasive as it has not spread into any surrounding breast tissue. LCIS isn't life-threatening, but having LCIS can increase a woman's risk of developing invasive breast cancer later on in life.

If a woman with LCIS develops an invasive breast cancer, it doesn’t typically happen within a few years. Rather, it is more likely to happen over the long-term - in 10, 15, or 20 years or even beyond that. A woman with LCIS is considered to be at elevated risk for developing breast cancer for the rest of her life.

Benign breast conditions

If you've been diagnosed with certain benign (not cancer) breast conditions, you may have a higher risk of breast cancer. There are several types of benign breast conditions that affect breast cancer risk

Benign breast disease (BBD) or “fibrocystic disease” are general terms applied to a range of changes in breast tissue. These changes can be difficult to distinguish clinically from invasive breast cancer until a biopsy is conducted for definitive diagnosis. BBD is a fairly common diagnosis and there are a number of types of BBD. BBD is usually detected before menopause.

Women with biopsy-confirmed BBD have been shown to have an overall modest increased risk of subsequent breast cancer. The risk is higher if you have been diagnosed with atypical hyperplasia (a type of BBD), and much lower for other types.

Having dense breasts

Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Someone is said to have dense breasts when their mammogram shows they have more glandular and fibrous tissue, and less fatty tissue.

Breast density only describes how breasts look on a mammogram. It isn’t a measure of how the breasts feel, and it cannot be determined in a clinical exam by a doctor.

Breast density can be a risk factor for two reasons. First,  mammograms of dense breasts can be harder to read than mammograms of less dense breasts. This can mean that there is a greater chance that cancers may be missed (or ‘masked’) on a mammogram. Second, research has also shown that women with very dense breasts have a greater chance of developing breast cancer than women with less dense breasts.

More research is needed to understand how to reduce this risk.  Currently, screening centres do not routinely advise women of their breast density. This is because there is still no reliable method for measuring density.  If you are interested in getting more information about your breast density, you may be able to ask your screening centre or GP if they can advise you. Our breast density page is also a helpful source of further information.

Radiation to chest or face before age 30

If you had radiation to the chest to treat another cancer (not breast cancer), such as Hodgkin's disease or non-Hodgkin's lymphoma, you have a higher-than-average risk of breast cancer. If you had radiation to the face as an adolescent to treat acne (something that’s no longer done), you are at higher risk of developing breast cancer later in life.

Pregnancy history

Women who haven’t had a full-term pregnancy or who have their first child after age 30 have a higher risk of breast cancer compared to women who gave birth before age 30.

Menstrual history

Women who started menstruating (having periods) younger than age 12 have a higher risk of breast cancer later in life. The same is true for women who go through menopause when they're older than 55.

Diethylstilboestrol

Diethylstilboestrol (DES) is a form of oestrogen that was commonly given to Australian women from the mid-1940s until the early 1970s to help prevent miscarriages and other pregnancy complications. It is no longer available for use in Australia.

In the early 1970s, DES was found to be linked to vaginal and cervical cancers in a small number of women who were exposed to DES in the womb.

Even though the majority of women exposed to DES won't experience any health issues, research shows that women who took DES while pregnant may have a small increased risk of breast cancer.

Research also shows that daughters of women who took DES during pregnancy may have a slightly increased risk of breast cancer after the age of 40 years.

If you used DES while you were pregnant, or are a daughter of a woman who took DES, and are 40 years or older you are encouraged to have an annual mammogram.

It's also important to be breast aware and to report any breast changes to your doctor, regardless of whether or not you have had a recent mammogram.

Cancer Council NSW has more information available on their website in the diethylstilboestrol (DES) and cancer fact sheet.

Using the oral contraceptive pill

A number of studies link the use of the oral contraceptive pill with a higher risk of breast cancer, especially among younger women. However, these studies also showed that this risk reduces over time once you stop taking the pill.

Using HRT (Hormone Replacement Therapy)

Studies have shown that current or recent past users of HRT have a higher risk of being diagnosed with breast cancer. However, these studies also showed that this risk reduces over time once you stop.

More information