Causes and risks


Causes and risk factors


The causes of breast cancer are not fully understood. This means that it is difficult to say why one woman may develop breast cancer and another may not.


Risk factors can change the likelihood that someone may develop breast cancer. There are some risk factors that you cannot do anything about, although there are others that you can change.


The risk of developing breast cancer increases as you get older. Breast cancer risks increase mostly amongst peri-menopausal women over 50 who are entering the menopause. Eight out of 10 cases of breast cancer occur in women over 50.


All women between 47 and 74 years of age should be screened for breast cancer every three years as part of the NHS Breast Screening Programme. Women over the age of 70 are still eligible to be screened and can arrange this through their GP or local screening unit.


Family history

If you have close relatives who have had breast cancer or ovarian cancer, you may have a higher risk of developing breast cancer. However, as breast cancer is the most common cancer in women, it is possible for it to occur more than once in the same family by chance.


Most breast cancer cases are not hereditary (they do not run in families). However, particular genes, known as BRCA1 and BRCA2, can increase your risk of developing both breast and ovarian cancers. It is possible for these genes to be passed on from a parent to their child. A third gene (TP53) is also associated with increased risk of breast cancer.


If you have, for example, two or more close relatives from the same side of your family (such as your mother, sister or daughter) who have had breast cancer under the age of 50, you may be eligible for breast cancer mamogram or MRI surveillance. Furthermore, you may be referred for genetic screening to look for the genes that make developing breast cancer more likely. If you are worried about your family history of breast cancer, discuss it with your GP or breast cancer Consultant.


Previous diagnosis of breast cancer

If you have previously had breast cancer or early non-invasive cancer cell changes contained within breast ducts, you have a higher risk of developing it again, either in your other breast or in the same breast as a second event.


Previous benign breast lump

A benign breast lump does not mean that you have breast cancer, but certain types of these lumps may slightly increase your risk of developing breast cancer. Certain benign changes in your breast tissue, such as atypical ductal hyperplasia (cells growing abnormally in ducts) or lobular carcinoma in situ (abnormal cells inside your breast lobules), can make getting breast cancer more likely.


Breast density

Your breasts are made up of thousands of tiny glands (lobules), which produce milk. This glandular tissue contains a higher concentration of breast cells than other breast tissue, making it denser. Women with more dense breast tissue may have a higher risk of developing breast cancer because there are more cells that can become cancerous.


Dense breast tissue can also make a breast scan (mammogram) harder to read because it makes any lumps or areas of abnormal tissue harder to detect. Younger women tend to have denser breasts. As you get older, the amount of glandular tissue in your breasts decreases and is replaced by fat, causing your breasts to become less dense.


Exposure to oestrogen

In some cases, breast cancer cells can be stimulated to grow of the female hormone, oestrogen. Your ovaries, where your eggs are stored, begin to produce oestrogen when you start puberty in order to regulate your periods.


Your risk of developing breast cancer may rise slightly with the amount of oestrogen that your body is exposed to. For example, if you started your periods at a young age and entered menopause at a late age, you will have been exposed to oestrogen over a longer period of time. In the same way, not having children, or having children later in life, may slightly increase your risk of developing breast cancer because your exposure to oestrogen is uninterrupted by pregnancy.


Being overweight or obese

If you have been through the menopause and are overweight or obese, you may be more at risk of developing breast cancer. This is thought to be linked to the amount of oestrogen in your body, as being overweight or obese after the menopause causes more oestrogen to be produced. Obesity increases the risk of postmenopausal breast cancer. A lack of physical activity (less than 150 minutes a week) is also a risk factor for developing breast cancer. Studies have shown that women whose diets are high in fat are more likely to get the disease, and women with a high fibre diet are less likely to develop breast cancer.



Your risk of developing breast cancer can increase with the amount of alcohol you drink. Research shows that, for every 200 women who regularly have two alcoholic drinks a day, there are three more women with breast cancer compared with women who do not drink at all. According to Cancer Research UK, more than 6% of breast cancers in UK women in 2010 were linked to alcohol consumption, with the risk increasing as the amount of alcohol consumed increases.



Certain medical procedures that use radiation, such as X-rays and CT scans, may slightly increase your risk of developing breast cancer. If you had radiotherapy to your chest area for Hodgkin's lymphoma when you were a child, you should have already received a written invitation from the Department of Health for a consultation with a breast cancer Consultant to discuss your increased risk of developing breast cancer. See your GP or breast cancer Consultant, if you were not contacted or you did not attend a consultation.


If you currently need radiotherapy for Hodgkin's lymphoma, your specialist should discuss the risk of breast cancer before your treatment begins.


Hormone replacement therapy (HRT)

Hormone Replacement Therapy (HRT) is associated with a slightly increased risk of developing breast cancer. Both combined HRT and oestrogen-only HRT can increase your risk of developing breast cancer, although the risk is slightly higher if you take combined HRT (oestrogen and progesterone).


It is estimated that there will be an extra 19 cases of breast cancer for every 1,000 women who are taking combined HRT for 10 years. The risk continues to increase slightly the longer you take HRT, but returns to normal once you stop taking it.