Risks and causes of breast cancer
Anything that increases the risk of getting a disease is called a risk factor.
Different cancers have different risk factors. Having one or more of these risk factors doesn’t mean that you will definitely get breast cancer.
Many people who have these factors never get it and some people with no risk factors develop it.
Risk factors for breast cancer include:
Women who are overweight after their 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 they gain more weight.
Keeping a healthy weight reduces the risk of at least 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 . 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
Combined HRT slightly increases the risk of breast cancer. But this risk is small. The risk of breast cancer is higher if you are using combined HRT compared to oestrogen only HRT. For oestrogen only HRT, there is little or no increased risk of breast cancer.
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
The following are risk factors that you are unable to change.
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 what your breast and chest are like, so you can notice a change that isn't normal for you.
Read about finding breast cancer early
Some people have a higher risk of developing breast cancer than the general population because family members 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
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 running in the family.
There are some people have an increased risk of breast cancer because they have an inherited gene change. We know about several gene changes that can increase breast cancer risk and there are tests for some of them. Having one of these gene changes means that you are more likely to get breast cancer than someone who does not. But it is not a certainty.
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 change (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 changes are not common. Only around 1 in every 450 people have a faulty BRCA1 or BRCA2 gene.
Examples of other inherited gene faults or conditions that may increase your risk of developing breast cancer include:
PALB2 gene
ATM gene
CHEK2 gene
, this syndrome is caused by a fault in the TP53 gene
, this syndrome is caused by a fault in the STK11 gene
PTEN Hamartoma tumour syndrome
RAD5 1 gene
Find out more about family history and inherited gene faults
Ionising radiation includes tests such as , and treatment such as .
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 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 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 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 treatment can be successful. Also, radiotherapy treatments are now more focused than in the past.
Women with 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 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)
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.
Breast lumps with an overgrowth of cells (proliferation) but without abnormal (atypical) cells increase the risk of breast cancer compared to the average risk.
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.
Find out about ductal carcinoma in situ
LCIS stands for lobular carcinoma in situ.
Find out about 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.
You have an increased risk of breast cancer if your periods started early. This means before the age of 12. Having a late can also increase your breast cancer risk. This means after the age of 55.
This increased risk is likely due to longer exposure to the hormone .
Levels of 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 , 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 , 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
Some factors might increase the risk of breast cancer but there is not enough evidence to be sure.
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
Stories about possible cancer causes are often in the media and it can be hard to know what’s true and what’s not. You may have heard of something that isn’t included here. This is because we only include a risk factor in this information if it is supported by good quality evidence.
Find out about common cancer myths and questions on the causes of cancer
Some factors can reduce the risk of breast cancer.
Read about factors that can reduce the risk
We have very detailed information for health professionals about breast cancer risks and causes.
For detailed information go to the Cancer Statistics section
This page is due for review. We will update this as soon as possible.
Last reviewed: 30 Jun 2023
Next review due: 30 Jun 2026
Symptoms of breast cancer include a lump in the breast or changes in the size, shape or feel of your breast. See your GP if you have any of these symptoms or any other symptoms of breast cancer.
You usually start by seeing your GP. Your GP will examine you and may refer you to a specialist breast clinic. Or you may have had breast changes picked up through breast screening.
The stage tells you how big your cancer is and whether it has spread. The grade means how abnormal the cells look under a microscope.
There are different types of breast cancer and breast conditions, including breast cancer in men, and conditions related to breast cancer.
There are some things that can help to reduce the risk of breast cancer, this includes keeping a healthy weight, eating a healthy diet and being physically active.
Find out about breast cancer, including symptoms, diagnosis, treatment, survival, and how to cope with the effects on your life and relationships.
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