Causes and risk factors

Currently, the causes of breast cancer are not fully understood. It is difficult to say why some woman develop breast cancer and others do not.Understanding causes and risk factors are important steps towards the prediction and prevention of breast cancer.


The risk of developing breast cancer increases as you get older. Breast cancer risks increase mostly amongst  women over 50 who are entering the menopause. Eight out of 10 cases of breast cancer occur in women over 50. This is why mammogram surveillance increases at the age of 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.


Research suggests that smoking increases the risk of breast cancer. Risk appears to be greater if you started smoking at a younger age. Risk appears to be greater for heavy lifetime smokers.

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. 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. 

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 mammogram. 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.

Benign breast lumps

Benign breast lumps do not mean that you have breast cancer, but certain types of these lumps may slightly increase your risk of developing breast cancer. Two examples of such lumps are fibroadenomas and breast cysts, both of which are completely harmless.

Women who have multiple cysts over a period of several years do have a slightly increased risk of breast cancer. If you are in this category, it is advisable to continue having regular mammograms and check-ups. More unusual types of breast lumps that have an associated increased risk of breast cancer are known as ‘proliferative’ breast disease or ‘atypical hyperplasia’ again regular mammograms are advisable.

Breast density

Women with more dense breast tissue may have a higher risk of developing breast cancer because there are more cells that can become cancerous.

Younger women tend to have denser breasts. which is why generally mammograms are not performed on women under 40 years of age. 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.

The density of breast tissue can be calculated by looking at a standard mammogram. Women with denser breasts have a higher risk of breast cancer compared to those with less dense breast tissue. Part of this increased density is related to genetic factors and part to hormonal factors (such as menopausal status or being on HRT).

Overweight or obese

Being overweight and gaining weight over adult life can increase the risk of developing breast cancer.   A lack of physical activity 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. Studies suggest that an overall healthy diet is most important, as well as being a healthy weight, taking regular exercise and moderating alcohol intake.


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.

A mammogram produces the same radiation as a dozen flights across the Atlantic

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.

More information on causes of breast cancer – NHS

More information on causes of breast cancer – Breast Cancer Now