Risk factors

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

Breast cancer is the most common cancer affecting Australian women. The risk of being diagnosed with breast cancer over a lifetime is 1 in 7 for women.

As with many other diseases, your risk of breast cancer increases as you get older. Although breast cancer can occur in younger women, most breast cancers occur after menopause. About three quarters (75 per cent) of breast cancer cases occur in women aged 50 years and over. 

Most people 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. 

Around 5 to 10 per cent of breast cancers occur in people who have inherited a single gene abnormality (mutation) from their mother or father. These faulty genes are rare, but the risk of breast cancer (and other cancers including ovarian and prostate cancers) for a person who inherits a faulty gene is higher.  

Most inherited cases of breast cancer are associated with mutations in two genes called BRCA1 (BReast CAncer gene one) and BRCA2 (BReast CAncer gene two).  Everyone has BRCA1 and BRCA2 genes. The function of these genes is for cell repair and to keep breast, ovarian and other cells growing normally. People who inherit an abnormal BRCA1 or BRCA2 gene means these genes don’t function normally and they have an increased risk of cancer particularly breast, ovarian and fallopian tube cancer.  

There are also a number of other even less common inherited gene abnormalities that increase the risk of developing breast cancer. Genetic tests are available to see if you have inherited an abnormal gene. Talk to your GP if you have a family history of cancers and are concerned about your risk. 

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

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

Fatty tissue is the body’s main source of oestrogen after menopause. Having more fatty tissue means higher oestrogen levels in the body, which may increase breast cancer risk. 

Regularly drinking alcohol is associated with an increased risk of breast cancer. Limiting the amount of alcohol you drink can reduce your risk of breast cancer.  

There does not appear to be a "safe" level of regular alcohol consumption for risk of breast cancer, according to the evidence. Alcohol may increase risk for breast cancer in a number of ways, including helping cancer-causing molecules to enter cells or damaging cell DNA. Alcohol is also thought to increase levels of the hormone oestrogen, which can influence breast cancer risk. For more information see Cancer Australia's Breast Cancer Risk Factors.

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-blocking therapy medicines. 

People 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) and lobular carcinoma in situ (LCIS).  Find more about non-invasive breast cancers at Types of breast cancer.

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.

For example, people who have atypical hyperplasia or lobular neoplasia have an increased risk of breast cancer. Most benign breast conditions do not increase the risk of breast cancer. 

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. 

People with very dense breasts have a greater chance of developing breast cancer than those with less dense breasts. See Breast density for further information.

If you had radiation to the chest or face 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.  

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

Women who started menstruating (having periods) younger than 12 years of age 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 years of age. 

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. 

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

Active people have reduced breast cancer risk compared with inactive people. National guidelines recommend at least 30 minutes of 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.  

Having children is associated with having a reduced risk of breast cancer. 

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.