Risk Factors


A fault in some genes may increase the risk of breast cancer. This doesn't mean that cancer will definitely happen but it means that the risk of developing cancer is higher than in the average person.



Types of faulty genes

The major breast cancer gene faults to be discovered were BRCA1 and BRCA2. In women carrying these gene faults there is a 45-90 % chance that they will get breast cancer at some time in their lives. There are also other genes that significantly increase a woman's risk of breast cancer, such as TP53 and PTEN.

If you have a strong family history of breast cancer it is possible to have a test for BRCA1, BRCA2, TP53 or PTEN. If you have a living relative with breast cancer they need to be tested for it first to try to find out which fault on the breast cancer genes might run in your family. This can take a few weeks or months. If a faulty gene is found the researchers can then look for that same gene fault in you. If there is no living relative you will still be offered the test if you have at least a 1 in 10 chance of having the faulty gene.

Researchers generally look at

  • The age your relatives were diagnosed with breast cancer (the younger they are, the more likely there is to be a faulty gene in the family)
  • Whether anyone had cancer in both breasts
  • If there are men in your family who have had breast cancer
  • If there is also ovarian cancer in the family

The affected family members must be close, blood relatives of yours and must all be from the same side of the family (so either your mother's relatives OR your father's).

To get a genetic test, you need to ask your GP for a referral to a specialist breast clinic. If they think you have a high risk of breast cancer, they will refer you to a specialist genetics service. There, the staff will talk to you about your risk and discuss the test with you. The test result usually takes a few weeks to come back.

Genetics testing (specifically BRCA1 and BRCA2 genes) have prompted women to opt for prophylatic (preventative) double mastectomies should they test positive.

This content is based on information published by Cancer Help UK, the patient information website of Cancer Research UK.

How common is breast cancer?

Approximately 50,000 women are diagnosed in the UK every year with breast cancer and nearly 400 men are also diagnosed with breast cancer. It is now the most common cancer in the UK (except for non melanoma skin cancer) and it is the most common cancer in women.

1 in 8 women in the UK will develop breast cancer during their lifetime. About 2 out of every 10 (20%) women are under 50 years old and the risk increases with age.

Something that increases your risk of getting a disease is called a risk factor. However, even if you have one or more of the risk factors below, it does not mean that you will definitely get breast cancer.


The risk of developing breast cancer increases as a woman get older. This is why mammograms as part of the national breast screening programme are advised. The UK screening programme sends invitations for screening to all women aged between 50 and 70. This is being extended to cover women from the ages of 47 to 73. You won't be invited to go for mammograms after you reach the age of 71, but you can ask your local breast cancer screening office to carry on inviting you every 3 years.

Family history

Having a mother or sister diagnosed with breast cancer approximately doubles the risk of breast cancer. But more than 8 out of 10 women who have a close relative with breast cancer will never develop it. However, if several members of your family have had particular types of cancer or if a relative was diagnosed with breast cancer at a young age, your risk of developing breast cancer may be higher.

Sex hormones and other hormones

The female sex hormone, oestrogen, and the male hormone, testosterone, can affect the development of breast cancer. Women tend to have small amounts of the male hormone testosterone in their bodies. Studies generally show that after the menopause women with higher levels of oestrogen and testosterone in their blood have a 2 to 3 times higher risk of breast cancer than women with the lowest levels of these hormones.

Hormone replacement therapy (HRT)

Many women in the UK take hormone replacement therapy (HRT) to reduce menopausal symptoms. There are 2 main types of HRT – combined HRT (oestrogen and progesterone) and oestrogen only HRT.

In 2003, researchers from Cancer Research UK looked at HRT and the risk of breast cancer in more than a million women. They showed clearly that HRT increases the risk of breast cancer while women take it and for up to 5 years afterwards. Other studies have also confirmed this. The Million Women study also showed that combined HRT (oestrogen and progesterone) is more likely to cause breast cancer than oestrogen only HRT.

A study published in December 2011 estimated that just over 3 out of 100 breast cancers in women in the UK in 2010 were linked to HRT use. This relates to around 1,530 cases.

Contraceptive pill

There seems to be a small increase in risk whilst a woman is taking it, but the increase in risk goes back to normal 10 years after stopping. Balanced against this, the pill seems to reduce the risk of some other cancers, such as ovarian and womb cancers.

Having children or having them early in life

Women who have children have a slightly lower risk of breast cancer than women who don't have children. The risk reduces further the more children you have. The age when you have your first child also has an effect. The younger you are when you have your first child, the lower your risk.

When you start and stop having periods

Starting your periods (menarche) at an early age has been linked with an increased risk of breast cancer. And if you have a late menopause this increases your breast cancer risk.

Ethnic group

Surveys in America and England have shown that white women have a higher risk of breast cancer than women from other ethnic groups. This is at least partly due to lifestyle factors. In patients know to be black, age at diagnosis is often younger at about 50 years compared with 62 years for those known to be white. In breast cancers picked up at mammography screenings (50-70 years) 56.3% of women known to be white had screen-detected breast cancers compared with 52.1% of women known to be Asian and only 44.6% of women known to be black. Black women are also more likely to have more aggressive breast cancers with poorer prognosis.

A previous breast cancer

We know that a woman who has had breast cancer has an increased risk of getting breast cancer in the other breast. Your specialist knows that too and will keep a close eye on you. If you do get a breast cancer in the other breast, it should be picked up quickly.

You will have some protection against getting another breast cancer if you are taking hormone modulation therapy (e.g. tamoxifen or anastrozole) to lower the risk of your breast cancer coming back.

Breast lumps with an overgrowth of cells (proliferation) but without abnormal (atypical) cells double the risk of breast cancer compared to the average risk.

About 5% show atypical hyperplasia. This means the cells are not cancer, but are growing abnormally. Atypical hyperplasia increases your risk of breast cancer by more than 4 times the average.

You should always get breast lumps checked out immediately to make sure they are not cancer.

Having dense breast tissue

Breast tissue density relates to how your breast tissue shows up on a mammogram. Women with dense breast tissue have less fat and more breast cells and connective tissue in their breasts. Because they have a greater proportion of breast cells, the risk of breast cancer is higher.

Your weight and height

Weight and height can both affect your breast cancer risk. If you are overweight before you've had your menopause, your risk of breast cancer is lower than average. But if you are overweight after menopause, your risk of breast cancer is higher than average. This is because women who are overweight ovulate less than average, so their breast cells may be exposed to lower levels of oestrogen. But after the menopause, your oestrogen levels are linked to the amount of body fat you have. The more fat you have, the higher your oestrogen levels are likely to be.

Taller women have an increased risk of breast cancer after the menopause. It's not clear why this is, but taller women may have more breast tissue, which might increase the risk.

Chest X-rays or radiotherapy

Chest X-rays give a very low dose of radiation and researchers estimate that around 60 cases of breast cancer in the UK each year are linked to diagnostic X-rays. Doctors balance this very small risk with the need to diagnose illness so that it can be properly treated. If you had a lot of chest X-rays in the past and are worried, talk to your doctor.

Radiotherapy treatment for breast cancer increases the risk of getting breast cancer in the other breast by a small amount. But this small risk is balanced by the need to treat the original breast cancer. If you had radiotherapy to your chest for Hodgkin's lymphoma in the past, you could be at increased risk of getting breast cancer.

If you need radiotherapy for Hodgkin's lymphoma your doctors will tell you about this risk. They will offer you breast screening if it is appropriate..


An overview study of 20 individual studies reported that women with diabetes have a small increase in their risk of breast cancer. This may be due to higher levels of insulin during the initial phase of diabetes. But people with diabetes often have a higher Body Mass Index (BMI) and a high BMI increases the risk of breast cancer for some people. So it is not clear why women with diabetes may have an increased risk. However, post menopausal women treated for diabetes with a medicine called metformin have a lower risk of breast cancer than women who don't have that treatment.

What you can do

Unfortunately there is little we can do about some of these risks, apart from be aware of them. But you can be aware of breast changes to look out for. It is important to attend for breast screening tests when you are invited.

Click here to visit the NHS Breast Screening Programme website.

This content is based on information published by Cancer Help UK, the patient information website of Cancer Research UK.