Risk factors for breast cancer

Women who are overweight after their ​menopause​ have a higher risk of breast cancer than women who are not overweight. Men also have an increased risk of breast cancer if they are overweight or obese. For both men and women, the risk increases as more weight is gained. 

Body mass index (BMI) is a measure that uses your height and weight to work out whether you are a healthy weight. For most adults, an ideal (BMI) is between 18.5 to 24.9. Being overweight means having a BMI of between 25 and 30. Obesity means being very overweight with a BMI of 30 or higher.

Keeping a healthy weight reduces the risk of 13 different types of cancer including breast cancer. Ways to keep a healthy weight include being physically active and eating a healthy, balanced diet.

Find out more about obesity and cancer

Drinking alcohol increases the risk of breast cancer in women. The risk increases with each extra unit of alcohol per day. The number of units in a drink depends on the size of the drink, and the volume of alcohol.

There is no safe level of alcohol, so the more you can cut down the more you can reduce your risk. The latest UK government guidelines advise drinking no more than 14 units of alcohol a week.

Find out more about alcohol and cancer

There is a very small increased risk of breast cancer when you take the ​contraceptive pill​. This increase in risk goes back to normal 10 years after you stop taking it.

Remember that breast cancer is rare in young women. Most women who take the pill are 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.

Talk to your doctor about the benefits and risks of taking the contraceptive pill.

Read about the contraceptive pill and cancer

Many women take hormone replacement therapy (HRT) to reduce the symptoms of menopause. There are 2 main types of HRT: 

• combined HRT (oestrogen and progestogen) 

• oestrogen only HRT

Your risk of developing breast cancer increases when taking any type of HRT. But this risk is small. The risk of breast cancer is higher if you are using the combined HRT compared to oestrogen only HRT.

The slight increased risk of breast cancer gets higher the longer you use HRT. But it goes down over time when you stop taking it.

For many people the benefits of taking HRT can outweigh the risks. Talk this through with your doctor for your individual situation.

Read more about HRT and breast cancer risk

Smoking tobacco increases the risk of getting breast cancer. There is a small increased risk in women who smoke compared to those who have never smoked. 

It is never too late to stop smoking but the sooner you stop the better.

Find out about smoking and cancer

Most breast cancers occur in women over 50 and it is less common in women under 40. Whatever your age it is important to be breast aware. This means getting to know your breast and chest.

Read about finding breast cancer early

Some 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.

Having a mother, sister or daughter diagnosed with breast cancer increases the risk of breast cancer. This risk is higher when more close relatives have breast cancer, or if a relative developed breast cancer under the age of 50. But most women who have a close relative with breast cancer will never develop it.

Because cancer is common, most families will have at least one person who has or has had cancer. But having a couple of relatives diagnosed with cancer doesn’t mean there is a ​gene fault​ running in the family.

There are some people have an increased risk of breast cancer because they have an inherited gene fault. We know about several gene faults that can increase breast cancer risk and there are tests for some of them. Having one of these faulty genes means that you are more likely to get breast cancer than someone who doesn’t. But it is not a certainty. 

BRCA1 and BRCA2 gene

Everyone has BRCA1 and BRCA2 genes. BRCA stands for BReast CAncer gene. These genes stop cells in our body from growing and dividing out of control. If there is a fault (mutation) in these genes, it means that cells can grow out of control. This can lead to developing several cancers including breast cancer.

BRCA1 and BRCA2 gene faults are not common. Only around 1 in every 450 people have a faulty BRCA1 or BRCA2 gene.

Examples of other inherited gene faults or ​genetic​ conditions that may increase your risk of developing breast cancer include:

• PALB2 gene

• ATM gene

• CHEK2 gene

• ​Li-Fraumeni syndrome​ , this syndrome is caused by a fault in the TP53 gene

• ​Peutz Jeghers Syndrome (PJS)​ , this syndrome is caused by a fault in the STK11 gene

• PTEN Hamartoma tumour syndrome

Find out more about family history and inherited gene faults

Ionising radiation includes tests such as x-rays and CT scans and treatment such as radiotherapy.

Ionising radiation includes tests such as x-rays and CT scans and treatment such as radiotherapy.

X-rays and mammograms

Exposure to radiation is known to increase the risk of many types of cancer. 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 is very small.

Many women worry about having mammograms as part of breast screening because it exposes them to x-rays. But the amount of radiation you have with a mammogram is very small.

Find out about breast screening

Radiotherapy

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 area to treat another type of cancer your risk of developing breast cancer is higher than someone who hasn't had radiotherapy. This is especially so for women who have had chest radiotherapy for Hodgkin lymphoma in the past.

If you need radiotherapy for Hodgkin lymphoma or any other type of cancer your doctors should tell you about this risk. They will offer you breast screening if it is appropriate. Talk to your doctor if you are unsure if you should have screening. 

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.

Women with ​diabetes​ have a small increase in their risk of breast cancer, although we are not sure why.

Breast cancer risk is higher in women with the most dense breast tissue compared to less dense tissue. Women with dense breast tissue have less fat and more breast cells and connective tissue in their breasts.

Our ​genetic​ make up affects breast density.

Benign breast disease means there is a change in the breast that is not cancer.

There are 3 types:

• non proliferative

• proliferative without atypia

• proliferative with atypia (atypical hyperplasia)

Non proliferative

Breast disease that is not growing and where the cells are not dividing is called non proliferative. It doesn’t usually increase the risk of breast cancer. But if you have a strong family history of breast cancer you might have a small increased risk.

Proliferative without atypia 

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

Atypical hyperplasia

This means the cells are not cancer but are growing abnormally. Atypical hyperplasia can increase your risk of breast cancer.

It is not common so 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 about it.

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

Find out more about atypical hyperplasia

DCIS and LCIS are changes within the breast tissue that might develop into breast cancer in some women. DCIS stands for ductal carcinoma in situ. LCIS stands for lobular carcinoma in situ.

Women with a diagnosis of DCIS or LCIS have double the usual risk of invasive breast cancer in the same or other breast. But it is important to remember that most women with LCIS or DCIS will not develop invasive cancer.

Find out about ductal carcinoma in situ

Find out about lobular carcinoma in situ

You have an increased risk of breast cancer if your periods started early (before the age of 12). Having a late ​menopause​ (after the age of 55) can also increase your breast cancer risk. 

This increased risk is likely due to longer exposure to the hormone ​oestrogen​ .

Levels of ​sex hormones​ can increase breast cancer risk. These hormones include:

• oestrogen

• progesterone

• testosterone

The male hormone, testosterone, can affect the risk of breast cancer. Women have small amounts of the male hormone testosterone in their bodies.

After the ​menopause​ , women with higher levels of oestrogen and testosterone in their blood may have a higher risk of breast cancer.

Women with higher levels of testosterone in their blood before menopause have a higher risk of breast cancer.

There is an increased risk of breast cancer in women with higher levels of a hormone called insulin like growth factor 1 (IGF-1). It is not clear what controls levels of IGF-1 in the bloodstream. It is probably related to our ​genes​ , body weight, and how much exercise we do.

A large report found that the risk of breast cancer is higher in white women than any other ethnic group. This is at least partly due to lifestyle factors.

Having had breast cancer increases your risk of getting another breast cancer. It might occur in the same breast or in the other breast.

Your specialist will keep a close eye on you with regular check ups. So, a new cancer should be picked up early.  

Having other types of cancer can also increase your risk.

People who had radiotherapy to the chest for Hodgkin lymphoma when they were young have a higher breast cancer risk.

Breast cancer risk is also higher in people who have had any of the following:

• melanoma skin cancer

• lung cancer

• bowel cancer

• womb cancer

• a type of leukaemia called chronic lymphocytic leukaemia

There has been a lot of research into whether diet increases the risk of breast cancer. So far most findings have been inconclusive and inconsistent.

Research has looked at a number of foods including:

• fat

• dairy foods

• fibre

• fruit

• soya (soy)

Researching diet and breast cancer is very difficult because we all eat such a range of different foods in such differing amounts. A large study called EPIC (the European Prospective Investigation into Cancer) is looking at the links between lifestyle and cancer. It involves around 520,000 people in 10 European countries.

It's better to aim for a healthy, balanced diet rather than focus on any one food. Having a healthy balanced diet can help you work towards or maintain a healthy body weight. There is evidence that being overweight or obese after the menopause, can increase your risk of breast cancer.

Find out how to enjoy a healthy diet