Breast cancer risks

Around 3,704 women are diagnosed with breast cancer in Ireland each year. Breast cancer is the most common cancer in women in Ireland, after skin cancer. 1 in 7 women in Ireland develop breast cancer during their lifetime. It is most common in women over the age of 50, but you can get it at a younger age. It is important to know what the risks of breast cancer are. We can reduce some of our risk by changing our behaviour and lifestyle. For other risks, such as our family history, there is nothing we can do to change it but it is still important to know if this risk factor might affect us.


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.


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 as they divide. Most breast cancers occur in women over 50. It is extremely rare in women under 40. However, it is important to get into the habit of checking your breasts monthly from the age of 20 so that you know what is normal for you and are able to spot any changes as soon as they occur.

It is important to have mammograms as part of BreastCheck, the national breast screening programme. BreastCheck invites women aged 50 to 68 for a free mammogram on an area-by-area basis every two years. To check if you are on the BreastCheck register, click here or Freephone 1800 45 45 55. 

Family history

If your mother, sister or daughter was diagnosed with breast cancer, particularly at a young age, you have an increased risk of breast cancer. However, it is important to note that the majority of people diagnosed with breast cancer have no family history of the disease.

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 younger than 40 years of age (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 younger than 50 years of age.
  • 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 of age 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 of age
  • A type of brain tumour called glioma or childhoodadrenal 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

Having dense breasts-

Most women are aware of the common risk factors when it comes to breast cancer. However, many are not aware of the importance of breast density, which has been described as one of the most significant risk factors of all. Women with dense breasts have a higher proportion of fibroglandular and supportive tissue, whereas those with less dense breasts have a higher proportion of fat.

Breast density cannot be measured by look or feel, only by mammography, where dense breast tissue appears white and fatty breast tissue appears dark. Breast density can be categorised into four different types

          • Mostly fatty
          • Scattered density
          • Heterogeneously dense
          • Extremely dense
  • Breast density is one of the strongest independent risk factors for developing breast cancer, stronger even than age or family history, with women with ‘extremely dense’ breast tissue being four-to-six times more likely to develop breast cancer compared to women with ‘mostly fatty’ breasts. High breast density can also have the effect of ‘masking’ breast cancers, as they also show up as white on a mammogram, and are thus more difficult to see.
  • Breast density cannot be measured by look or feel, only by mammography, where dense breast tissue appears white and fatty breast tissue appears dark.
  • 10% of women between the ages of 40 – 74 have extremely dense breast and 35% have heterogeneously dense breast. These are the women who are at risk of a cancer not being picked up by mammogram as dense breast look white on a mammogram and cancer looks white on a mammogram.
  • Currently, women in Ireland going through the BreastCheck mammographic screening programme are not routinely informed about their breast density when receiving their results, and many are unaware of this important risk-factor.

For more information on breast density, please click here.


Assessing risk

If your GP refers you to a specialist breast clinic for assessment, the team work out your risk of developing breast cancer using your family history and individual factors. It may be that based on these factors your risk is the same as that of an average woman. If your risk is found to be moderate or high, you may be offered 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)
  • whether you have a moderate or high risk of developing breast cancer
  • 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


Breast cancer genes

Certain gene mutations that increase the risk of breast cancer can be passed from parents to children. 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 faulty genes but two that we know about, and can test for, are referred to as BRCA1 and BRCA2. These genes can greatly increase your risk of breast cancer and other cancers, but they don’t make cancer inevitable. If you have either of these genes, your risk of getting breast cancer by the age of 70 is between 45 to 65%.

It is important to remember that most breast cancers happen by chance. Only about 3 out of every hundred (3%) breast cancers 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.


Having had breast cancer

If you have had breast cancer, you have an increased risk of getting another breast cancer. The cancer may occur in the same breast or in the other breast. Your consultant is aware of this risk too and will monitor you. If you do get breast cancer again, it should be picked up quickly.

If you are taking hormone therapy to lower the risk of breast cancer coming back, this will provide you with some protection.


Having had other types of cancer

Breast cancer risk is increased in people who have had other cancers such as Hodgkin’s 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

Oestrogen (the female sex hormone) and testosterone (the male sex hormone), can affect the development of breast cancer. Women tend to have small amounts of 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.


Hormone replacement therapy (HRT)

Many women take hormone replacement therapy (HRT) to reduce menopausal symptoms such as hot flashes and sweating. There are 2 main types of HRT – combined HRT (oestrogen and progesterone) and oestrogen only HRT.

HRT is linked to a higher risk of breast cancer. Combined HRT (oestrogen and progesterone) is more likely to cause breast cancer than oestrogen only HRT. The longer HRT is used, the higher the risk. However, the risk returns to that of a woman who never used HRT (the average risk) within 5 years of stopping the hormones. Breast cancers in women taking some types of HRT are more likely to be found when they are bigger and have spread beyond the breast. This may be because taking HRT is also linked to increased breast density which can make it harder to find breast cancer on a mammogram.

To put the risk into numbers, if 10,000 women took oestrogen-only HRT for a year, it would result in up to about 8 more cases of breast cancer per year than if they had not taken hormone replacement therapy (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.


The contraceptive pill

The combined pill contains oestrogen which 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.

At the moment, there is little evidence that the risk of breast cancer with the Pill is increased more for women with a family history of breast cancer. Because a family history of breast cancer often goes hand in hand with a higher risk of ovarian cancer, the Pill’s protective effect against ovarian cancer would be beneficial. If your mother or sister has had breast cancer, make sure that your doctor is aware of this, especially before taking the Pill.

It is important to remember that the Pill can have positive health benefits and are often used by younger women who have less risk of breast cancer than women over 50. If you have concerns, speak to your GP about them and all your contraceptive options.


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 at an early age has been linked with an increased risk of breast cancer. If you have a late menopause this increases your breast cancer risk compared to women who have an earlier menopause. This is mainly due to longer life span exposure to hormones.


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.



Alcohol intake and smoking

Drinking alcohol has been consistently linked to an increased risk of developing breast cancer. The risk increases with the amount of alcohol consumed. For example, compared with a woman who does not drink, a woman who has 1 alcoholic drink a day has a very small increased risk while a women who has 2 to 5 drinks daily has a 1.5 increased risk of breast cancer. Other cancers, such as liver cancer, colon and rectal cancer and mouth cancer, are also linked with alcohol consumption.

A recent major study published in the British Medical Journal found that just one drink a day puts women at increased risk of breast and other alcohol-related cancers. People with a family history of cancer should consider giving up alcohol altogether because of the proven link between moderate drinking and alcohol-related forms of the disease, according to this study. In relation to cancer there is no safe limit of alcohol.

Whether you decide to give up or limit your alcohol intake, it is best for women not to drink more than 11 units of alcohol per week. Be mindful that one drink does not equal one unit. Large wine glasses hold 250ml, which is one third of a bottle. It means there can be nearly two units or more in just one glass.

Smoking tobacco also 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 getting breast cancer before the menopause (pre-menopausal breast cancer) may be higher than someone who had a lower birth weight.

Women who are overweight after the menopause have a higher than average risk of breast cancer. This may be 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. If you are apple shaped as opposed to pear shaped you are at higher risk of developing any kind of cancer. This is associated with more fat deposits around the abdomen.

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. 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 and mammograms does expose you to a small amount of radiation but the increase in risk is very small compared to the benefit of finding breast cancer early and treating it.

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.


Other medical conditions

Medical conditions that may increase breast cancer risk include diabetes and benign thyroid conditions. Speak to your doctor for more information.



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. If you have any concerns about any of this information talk to your GP.

Women have an increased risk of breast cancer if they took a drug called diethylstilbestrol during pregnancy between the 1940s and 1960s. Diethylstilbestrol 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. 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. Visit out page about breast cancer prevention for more information.  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.  You can watch our video on how to check your breasts here. It is important to attend for breast screening tests with BreastCheck when you are invited.