What are the risk factors for breast cancer?

Risk factors for breast cancer

A risk factor is anything that can increase your chance of developing a certain condition, such as breast cancer.  

Some risk factors can’t be changed. These are called non-modifiable risk factors, and include: 

• a family history of breast or ovarian cancer (ovarian cancer risk is often linked to breast cancer risk) 
• inherited genetic factors, such as a faulty or mutated gene 
• medical history, such as having previously had radiation therapy (for example, for Hodgkin Lymphoma) or another type of cancer 
• reproductive history, such as starting menstruation very young, reaching menopause late, or not having a baby 
• getting older 
• having dense breasts. 

Some risk factors can be changed. These are called modifiable risk factors, and include:  

• not exercising enough 
• smoking tobacco  
• drinking alcohol 
• being overweight or obese 
• taking some medicines, such as diethylstilboestrol (DES) or hormone therapy (including the birth control pill). 

Having one or more risk factors does not mean you will develop cancer. Many people have at least one risk factor but will never develop cancer, while others have no known risk factors but do develop cancer. Even if a person with cancer has a risk factor, it is usually hard to know how much it contributed to the development of their disease. 

Find out more about risk factors, or go to iPrevent, a breast cancer risk assessment tool which estimates your chance of developing breast cancer. You should discuss any results you are concerned about with your doctor. ^[1][2] 

Family history

You’re considered to have a family history of cancer if one or more close blood relative on the same side of your family has had cancer. Family history on your father’s side is just as important as on your mother’s side. 

Breast cancer risk goes up if: 

• you have multiple family members with breast cancer 
• your family members were young when first diagnosed 
• your family members with breast cancer are closely related to you. 

The increase in cancer risk is often small. But it can be greater if you have 3 or more first-degree relatives (such as parents or siblings) or second-degree relatives (such as grandparents) on the same side of the family who have had breast cancer or ovarian cancer.  

The risk is also increased if 2 or more relatives have other characteristics that relate to an increased risk, such as being diagnosed before the age of 50 or being of Ashkenazi Jewish descent. People of Ashkenazi Jewish heritage have an increased chance of inherited genetic factors that can cause breast or ovarian cancer. 

Because cancer is common, it is not unusual for more than one family member to develop cancer during their lifetime. This can happen by chance, or because of another factor.  

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.  

On the other hand, most women who develop breast cancer do not have an affected first-degree relative. Of those women with a family history who do develop breast cancer, most are diagnosed when aged over 50 years.  

Inherited genetic factors

Breast or ovarian cancer that is 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 a gene that stops that gene from working properly. This fault is called a ‘pathogenic variant’. 

Several pathogenic variants may be involved in the development of breast or ovarian cancer. The most common mutations are in the BRCA1 or BRCA2 genes. When normal, these genes prevent a woman from developing breast or ovarian cancer. Faulty BRCA1 or BRCA2 genes increase the risk of developing breast or ovarian cancer. 

Ashkenazi Jewish people are those with 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. This means that some gene faults that can cause breast or ovarian cancer are found more often in people with Ashkenazi Jewish heritage. 

Reduce your risk of getting breast cancer

Although some risk factors cannot be changed, you can still aim to reduce your risk of breast cancer by improving your diet, reducing your alcohol intake, maintaining a good weight and getting some exercise.  

It is also very important to detect breast cancer as early as possible, as treatment tends to be more successful for early breast cancer. You can help do this by: 

• being breast aware and knowing how to check your own breasts 
• participating in the BreastScreen Australia program 
• seeing a doctor as soon as possible if you find any changes. 

Read more about diagnosing breast cancer or breast cancer risk factors.