Definite breast cancer risks | Cancer Research UK
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Definite breast cancer risks

Researchers have identified a number of things that can affect your risk of breast cancer. Breast cancer risk increases with age. Your risk is increased if you've had breast cancer before, or if someone in your family has. You have a particularly increased risk if you carry a breast cancer gene. A history of some non cancerous breast diseases, or having had ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS), also increases the risk.

Hormonal factors

There are some hormonal factors that increase risk, including

  • Having higher levels of hormones in your blood after the menopause
  • Starting periods early and having a late menopause
  • Having no children or having them late in life
  • Taking hormone replacement therapy (HRT) or the contraceptive pill.

Lifestyle and past medical treatment

There are also some lifestyle factors that increase risk, including alcohol intake, body weight and night shift work. Some types of medical treatment can affect breast cancer risk, for example taking blood pressure medicines, or exposure to radiation, including treatment for Hodgkin lymphoma.


CR PDF Icon You can view and print the quick guides for all the pages in the About breast cancer section.



How common breast cancer is

Around 49,900 women are diagnosed with breast cancer in the UK each year. And around 350 men are diagnosed. Breast cancer is now the most common cancer in the UK (excluding non melanoma skin cancer) and by far the most common cancer in women.

1 in 8 women in the UK develop breast cancer during their lifetime. Most of the women who get breast cancer have had their menopause, but about 2 out of every 10 (20%) are under 50 years old.


What risk factors are

Anything that increases your risk of getting a disease is called a risk factor. Different cancers have different risk factors. This page discusses the risk factors for breast cancer. Even if you have one or more of the risk factors below, it does not mean that you will definitely get breast cancer.

Breast cancer risk impact statement


Getting older

Like most cancers, the risk of developing breast cancer increases as women get older. As we get older the cells in our body have had more chance to make mistakes when they were dividing. Most breast cancers occur in women over 50 and it is extremely rare in women under 40.

It is important to have mammograms as part of the national breast screening programme as soon as you are old enough. The UK screening programme sends invitations for screening to all women aged between 50 and 70. They are extending this 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

A small number of people have a higher risk of developing breast cancer than the general population because other members of their family have had particular cancers. This is called a family history of cancer. It relates to past and present cancers of blood relatives (people related by birth, not marriage). This increased risk may be due to an inherited faulty gene.

Having a mother, sister or daughter 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. 

Cancer Research UK research has suggested that identical twins of women already diagnosed with breast cancer have a 1 in 3 risk of getting breast cancer themselves at some point in their lives. The risk for women generally is 1 in 8 over the whole lifetime. So, according to this research, identical twin sisters of diagnosed breast cancer patients have around 3 times the risk of the average woman. Research from America has estimated the increase in risk as 4 times the risk of the average woman.

The National Institute for Health and Care Excellence (NICE) has guidelines that identify family histories that could increase your risk of breast cancer. It recommends that your GP should refer you to a specialist breast clinic for assessment if you have any of the following:

  • One first degree female relative diagnosed with breast cancer aged younger than 40 (a first degree relative is your parent, brother or sister, or your child)
  • One first degree male relative diagnosed with breast cancer at any age
  • One first degree relative with cancer in both breasts where the first cancer was diagnosed aged younger than 50
  • Two first degree relatives, or one first degree and one second degree relative, diagnosed with breast cancer at any age (second degree relatives are aunts, uncles, nephews, nieces, grandparents, and grandchildren)
  • One first degree or second degree relative diagnosed with breast cancer at any age and one first degree or second degree relative diagnosed with ovarian cancer at any age (one of these should be a first degree relative)
  • Three first degree or second degree relatives diagnosed with breast cancer at any age

Your GP should also refer you if you have one first degree or second degree relative diagnosed with breast cancer when they were older than 40 years and one of the following

  • The cancer was in both breasts (bilateral)
  • The cancer was in a man
  • Ovarian cancer
  • Jewish ancestry
  • Sarcoma (cancer of the bone or soft tissue) in a relative younger than age 45 years
  • A type of brain tumour called glioma or childhood adrenal cortical carcinomas
  • Complicated patterns of multiple cancers diagnosed at a young age
  • Two or more relatives with breast cancer on your father's side of the family

Assessing risk

The specialist breast clinic team work out your risk of developing breast cancer using your family history and individual factors. After assessment they may tell you that your risk is much the same as the average woman. If your risk is found to be moderate or high, the breast team may offer you an appointment with a genetic counsellor. The counsellor can help you understand more about your risk. They will also offer you information about genetic testing.

If you have a raised risk

If your doctor or genetic counsellor think that you have a raised risk of breast cancer they will offer you screening. The screening may include yearly mammograms and possibly MRI scans. The screening you will have depends on

  • Your age
  • How dense your breasts are (if your breast tissue is dense it can make reading mammograms more difficult)
  • Your risk of developing breast cancer, that is whether you have a moderate or high risk
  • What your risk is of having a particular gene change if you haven't had a test 
  • Whether you have had a test that showed a genetic change

More information about family history of breast cancer

You can read the NICE guidance on risk of breast cancer in people with a family history. On this website there is detailed information about breast screening and who should be referred.

If you are worried that several members of your family have had breast or ovarian cancer, the best thing to do is talk to your GP. If you like, you could print off this page and take it with you.


Breast cancer genes

If you have a very strong family history, there may be a faulty gene in your family that increases your risk of breast cancer. There are probably several gene faults that can increase breast cancer risk. We can test for 2 of them, BRCA1 and BRCA2. Your risk of getting breast cancer by the age of 70 if you have either of these breast cancer gene faults is between 45 to 65%. 

Having one of these faulty genes means that you are more likely to get breast cancer than someone who does not have the gene fault. But it is not a certainty. It is also possible to test for the faulty TP53 gene and PTEN gene, which are much rarer than BRCA mutations, but can increase the risk of breast cancer. In this section there is information about breast cancer genes, getting tested, and your options if you have a faulty gene.

Remember that most breast cancers happen by chance. Only about 3 out of every hundred (3%) are related to a known inherited breast cancer gene. The older that you or your relatives are when diagnosed, the less likely it is that an inherited gene is the direct cause. 


A previous breast cancer

We know that a woman who has had breast cancer has an increased risk of getting another breast cancer. The cancer may occur in the same breast or 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 therapy to lower the risk of your breast cancer coming back.


Having cancer other than breast cancer

Breast cancer risk is increased in people who have had other cancers such as Hodgkin lymphoma. The risk is further increased if people were diagnosed when they were young and if they had radiotherapy treatment rather than chemotherapy.

Breast cancer risk is also higher in people who have had melanoma skin cancer, lung cancer, bowel cancer, womb cancer, and a type of leukaemia called chronic lymphocytic leukaemia.


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 menopause women with higher levels of oestrogen and testosterone in their blood have a risk of breast cancer that is double that of women with the lowest levels. 

Before the menopause, levels of oestrogen vary during the menstrual cycle and studies have not shown clearly that these hormones affect the risk of breast cancer in this group of women. Many of the major risk factors for breast cancer can be explained through their effect on hormone levels.

Studies also show an increased risk of breast cancer in with higher levels of a hormone called insulin like growth factor 1 (IGF-1). We are not sure what controls levels of IGF-1 in the bloodstream, but it is probably related to our genes, body weight, and how much exercise we do.


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. About 3 out of 4 of these extra breast cancers are linked to the use of combined oestrogen and  progesterone HRT. And 1 out of 4 are linked to oestrogen only HRT.

HRT can have some health benefits and so if you are worried about taking it, you can talk to your doctor about the benefits and risks in your individual situation.

There is detailed information about HRT and breast cancer risk in the question and answer section.

HRT impact statement


The contraceptive pill

The combined pill contains oestrogen. Oestrogen can stimulate breast cancer cells to grow. In theory, taking extra oestrogen could trigger a breast cancer to develop. Several large studies have looked at whether the pill can increase the risk of breast cancer. The overall picture seems to be that there is a small increase in risk while you are taking it. But the increase in risk goes back to normal 10 years after you've stopped taking it. Balanced against this, the pill also seems to reduce the risk of some other cancers, such as ovarian and womb cancers.

We don't really know if taking the pill increases the risk of breast cancer for women who have a family history of breast cancer. Some research says that it may increase breast cancer risk in these women. Other studies have found that it makes no difference. So we need more research to find this out.

It can be difficult to make sense of all this research. It is important to remember that breast cancer is rare in young women and the age groups most often using the pill are women in their late teens, twenties and early thirties. So a small increase in this risk during the time women take the pill means very few extra cases of breast cancer.


Not having children or having them later in life

Women who have children have a slightly lower risk of breast cancer than women who don't have children. And the risk reduces further the more children you have. Your 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 (before the age of 12) has been linked with an increased risk of breast cancer. And if you have a late menopause (after the age of 55) this increases your breast cancer risk compared to women who have an earlier menopause.


Ethnic group

Statistical 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. 



DCIS stands for ductal carcinoma in situ. This is when breast cancer cells are completely contained within the breast ducts and have not started to spread into (invade) the surrounding breast tissue. It is sometimes called pre invasive breast cancer. LCIS stands for lobular carcinoma in situ. It means there are some abnormal cells in the lobules of the breast.

Studies show that women with a diagnosis of DCIS or LCIS have a risk of invasive breast cancer in the same or other breast that is approximately double that of women in the general population. One study showed that women with a previous carcinoma in situ of the breast have a 16% (about 1 in 6) risk of developing breast cancer within 10 years. But, even so, most women with LCIS or DCIS will not develop invasive cancer. 

High grade DCIS and a type of LCIS called pleomorphic LCIS are more likely to develop into invasive breast cancer than other types of DCIS or LCIS. If you do have LCIS or DCIS, your doctor will want you to have check ups regularly afterwards. There is information about LCIS and DCIS in this section.


Benign breast disease

There are 3 types of non cancerous (benign) breast conditions

  • Non proliferative
  • Proliferative without atypia
  • Proliferative with atypia (atypical hyperplasia)

Breast disease that is not growing and where the cells are not dividing is called non proliferative and does not usually increase the risk of breast cancer. But if you have a strong family history of breast cancer it may increase the risk by a small amount.

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

About 1 in 20 breast lumps (5%) show atypical hyperplasia. This means the cells are not cancer, but are growing abnormally. Atypical hyperplasia increases your risk of breast cancer by about 3 times the average. Atypical hyperplasia is uncommon and if you haven't been told that your breast lump showed these changes, it probably didn't. But if you are worried, you can ask your doctor to check the biopsy result and let you know.

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. 

A recent overview of studies (meta analysis) reported that women with the most dense breasts had almost five times the risk of breast cancer of women with the lowest density. There is some evidence that ultrasound can be a useful test alongside mammography for diagnosing breast cancer in women with dense breasts. Breast ultrasound may be able to pick up a breast cancer that a mammogram has missed. MRI scans may also be helpful in finding cancers in denser breast tissue in younger women.


Alcohol intake and smoking

Drinking alcohol has been shown to increase the risk of breast cancer by a small amount. Two large combined reviews of the published evidence and the UK Million Women Study showed an increase in risk of about 7 to 12% with every extra unit of alcohol per day. One unit is a half pint of beer, a small glass of wine, or a measure of spirits. Alcohol in moderation can have some beneficial effects on the risk of heart attack or stroke. But to be on the safe side, it is best for women not to drink more than 14 units of alcohol per week. 

Smoking tobacco increases the risk of breast cancer. The risk increases with the number of cigarettes smoked. The risk is especially increased in women who started smoking before the age of 20 or before the birth of their first child.


Your weight and height

Weight and height can both affect your breast cancer risk.

If you had a higher weight at birth, your risk of pre menopausal breast cancer may be higher than someone who had a lower birth weight.

Women who are overweight before their menopause may have a slightly lower than average breast cancer risk, according to several meta-analyses. But one meta-analysis has shown that women who are overweight after menopause have a higher than average risk of breast cancer. 

Men who are overweight have a higher risk of breast cancer than men of normal weight.

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.


X-rays or radiotherapy

Exposure to radiation is known to increase the risk of many types of cancer. But most of this research has been in people who have been exposed to a lot of radiation, due to an atomic bomb explosion or a radiation accident. There is known to be a slight increase in risk in people who work with low doses of radiation over a long period of time – for example, X-ray technicians. But most of us are never exposed to enough radiation to make much difference to our risk.

Nowadays, doctors keep medical exposure to radiation as low as possible. They don't do X-rays or CT scans unless they really need to. And the amount of radiation used to take an X-ray or scan is very small, and lower than it used to be.

Radiation from chest X-rays

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.

Radiation from mammograms

Many women worry that having mammograms as part of breast screening exposes them to X-rays. But the amount of radiation used to take a mammogram is very small. The increase in risk is tiny compared to the benefit of finding and treating a breast cancer early. Many things we do expose us to slight increases in radiation (such as flying in a plane) but we don't always think it sensible to stop doing them.

Radiotherapy for breast cancer

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.

Radiotherapy for Hodgkin lymphoma

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 lymphoma your doctors will tell you about this risk. They will offer you breast screening if it is appropriate. Research has shown that 

  • If they were treated in childhood, between 1 in 7 and 1 in 3 women will get breast cancer at some point in the 25 years after their treatment
  • If they were treated in their 20s, between 1 in 7 and 1 in 4 women will get breast cancer at some point in the 25 years after their treatment

For women in general, about 1 in 50 will get breast cancer by the age of 50. So you can see that the risk for people treated for Hodgkin lymphoma is quite a bit higher. The individual risk for any woman will depend on the following factors.

  • Her age when she was treated
  • The total dose of radiotherapy she had
  • The amount of time that has gone by
  • Her age now

It is important to remember that second cancers are usually found early when they can be successfully treated. Also, radiotherapy treatments are now more focused than in the past. So if you had treatment recently, the risk of breast cancer is likely to be lower than for people who had treatment years ago.


Other medical conditions

Medical conditions that may increase breast cancer risk include diabetes and benign thyroid conditions.


An overview study (meta analysis) 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. 

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.

Benign thyroid conditions

Breast cancer risk is increased by about 3 times in women who have autoimmune thyroiditis. But breast cancer risk does not seem to be increased by having an overactive thyroid (hyperthyroidism) or underactive thyroid (hypothyroidism).



One study found that taking high blood pressure medicines for longer than 5 years increases the risk of breast cancer by a fifth. People treated for an overactive thyroid gland (Graves' disease) also have an increase in breast cancer risk.

Women have an increased risk of breast cancer if they took a drug called diethylstilbestrol during pregnancy between the 1940s and 1960s. Diethylstilboestrol is an oestrogen like drug that is no longer used. Doctors gave it from 1945 to about 1970 to women who were at risk of miscarriage.

The drug digoxin is used to treat heart failure and may increase breast cancer risk. However, the risk may decrease when people stop taking it.


Dietary fat

Women who have a high amount of fat in their diet have a higher risk of breast cancer than women with lower dietary fat levels according to a meta-analysis. Eating higher amounts of saturated fats also increases breast cancer risk. 


Shift work

Some studies have shown that women who do night shift work have a slight increase in breast cancer risk. Other studies show that sleeping longer reduces the risk of breast cancer. Some researchers think this may be because broken or shorter periods of sleep lowers levels of a hormone called melatonin.


Reducing your breast cancer risk

We can help to reduce our breast cancer risk by eating healthily, maintaining a healthy weight, not smoking, and drinking alcohol in moderation. Unfortunately there is little we can do about some of the other risks, apart from be aware of them. But you can be aware of breast changes to look out for. And it is important to attend for breast screening tests when you are invited.

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Updated: 12 August 2014