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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 iPrevent to help give youan understanding of your level of risk for developing breast cancer compared to the average risk for women your age. iPrevent provides personalised information about how to minimise your breast cancer risk. iPrevent is based on the latest international evidence and is the only Australian breast cancer risk calculator that has undergone rigorous testing. Your iPrevent results can be printed out for later discussion with your doctor if you need more advice.

Risk factors

There are many risk factors for breast cancer - some are things you can change and others are not. However, even women with unchangeable risk factors can do things to manager their breast cancer risk. For some advice on doing this, you can use iPrevent, talk to your doctor or visit our Reducing your risk page. 

Being a woman

Being a woman is the single biggest risk factor for developing breast cancer.

Breast cancer is the most common cancer affecting Australian women. In 2019, it is estimated that 19,371 women will be diagnosed.

This means that approximately 19,535 Australians will be diagnosed with breast cancer in 2019, an average of 53 people every day.

Men also make up the above figure, although they account for a small number. In 2019, it is expected that 164 men will be diagnosed with breast cancer.

Age

As with many other diseases, your risk of breast cancer increase as you get older. Although breast cancer can occur 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.

Height

Being tall is associated with a small increased risk of breast cancer. 

Family history

 

Most women who develop breast cancer do not have a strong family history. However, having one or more first-degree relatives or second-degree relatives on the same side of the family with breast cancer can increase your risk.

Faulty genes

Around 5% of breast cancers occur in women who have inherited  a single gene abnormality from their mother or father, and which  puts them at greater risk of developing breast cancer. These faulty genes are rare, but the risk of breast cancer for a woman who inherits one is high. 

The best known of these genes are  BRCA1 and BRCA2.  When normal these genes help to prevent cancer, so women who inherit an abnormal gene have an increased risk of cancer, particularly breast cancer and ovarian and fallopian tubecancer.

Abnormalities in BRCA1 or BRCA2 occur in about 1 in 400 (0.2%) Australian women, but they are more common in some ethnic groups – for example they occur in about 1 in 40 (2.5%)  people with Ashkenazi Jewish (Eastern Europe) heritage.

There are also  other, even less common, inherited gene abnormalities that increase the risk of developing breast cancer.

iPrevent can help you assess your family cancer history and advise you whether you might consider having it looked at more formally in a Family Cancer Centre. Certainly 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 (either your mother’s or father’s side) who have been diagnosed with breast cancer or ovarian cancer, you might consider asking your GP about referral to a Family Cancer Centre. For women with Ashkenazi Jewish heritage, this might be considered even if the family history is less strong.

See our page Breast cancer in the family for further information and advice.

 

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

The  link  between smoking and breast cancer is unclear, but 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 most  women with DCIS will never 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  increases a woman's risk of developing invasive breast cancer. Medication can substantially reduce the risk. See iPrevent and talk with your doctor for details.  

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.

Mammographic (or breast) density only describes how breasts look on a mammogram.

Women with very dense breasts have a greater chance of developing breast cancer than women with less dense breasts. Our Mammographic 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 may have an increased risk of breast cancer. If you had radiation to the face as an adolescent to treat acne(something that’s no longer done), you may have an increased  risk of developing breast cancer. A breast cancer risk expert can help you determine whether your risk is increased and what options you might have to reduce your risk.

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.

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 suggest  a woman’s breast cancer risk is increased while she is taking the  oral contraceptive pill and for up to 10 years after stopping it. For most young women in their 20s and 30s the increase in risk is small, but for older women and those with other strong risk factors (such as a faulty gene) the risk may be greater.

Using HRT (Hormone Replacement Therapy)

Studies have shown that women who use  combined HRT (oestrogen and progesterone together) for 5 years or more have a higher risk of being diagnosed with breast cancer. However, these studies also showed that this risk reduces over time once you stop.

Protective factors

There are some things that are associated with reduced breast cancer risk.

Exercise

Active women have reduced breast cancer risk compared with inactive women. National guidelines recommend at least 30 minutes of at least moderate intensity exercise most days of the week, aiming for 2.5 to 5 hours per week.  Moderate intensity exercise makes you puff. Muscle strengthening exercise 2 days a week are also recommended. You can talk with your GP about how you can best achieve this.  

Breastfeeding

Breastfeeding is encouraged because it has health benefits for babies and their mothers. Longer breastfeeding is associated with lower breast cancer risk. Australian guidelines suggest breastfeeding each baby for 12 months or longer if desired.

Medicine and Surgery

For women at increased risk of breast cancer medication has been clearly shown to substantially reduce breast cancer risk. Surgery is also an option for women at very high risk. 

More information