The exact cause of breast cancer is unknown. But certain things can increase your chance of developing it. These are called risk factors. The risk factors for invasive breast cancer and ductal carcinoma in situ (DCIS) are similar.
Having one or more risk factors does not mean you will definitely get breast cancer. And if you do not have any risk factors, it does not mean you will not get it.
Breast cancer is likely to be caused by a combination of different risk factors, rather than just one.
Having certain breast conditions can also increase the risk of developing breast cancer:
Lobular carcinoma in situ (LCIS)
Atypical ductal hyperplasia
This is when there are slightly abnormal-looking cells in the milk ducts in a small area of the breast.
Women with these non-cancerous (benign) conditions are usually monitored regularly, so any changes can be found early.
Dense breast tissue is when the breast is mostly made of glandular and connective tissue with very little fatty tissue.
Women whose mammograms show dense breast tissue have an increased risk of breast cancer compared with women whose mammograms show mainly fatty tissue.
The female hormones oestrogen and progesterone can affect your breast cancer risk. Factors that can increase your risk include the following:
- Taking hormone replacement therapy (HRT) for more than 5 years, especially if you are taking combined HRT (oestrogen and progesterone). When you stop HRT, your risk reduces again.
- Not having had children.
- Having had your first child after the age of 30.
- Not breastfeeding your children, or breastfeeding for less than a year in total.
- Starting your periods early (under the age of 12) or having a late menopause (after the age of 55).
- Taking the contraceptive pill. But the risk reduces if you stop taking it.
Most women who get breast cancer do not have a family history of it. Or if you have only one female relative diagnosed with breast cancer over the age of 40, your risk is unlikely to be very different from other women the same age as you.
But sometimes breast cancer can run in families. The chance of there being a family link is bigger when:
- a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer
- the family members are closely related
- the family members were diagnosed at a younger age
- a man in your family has been diagnosed with breast cancer.
Fewer than 1 in 10 breast cancers (10%) are thought to be caused by a change (alteration) in a gene running through the family. In hereditary breast cancer, BRCA1 and BRCA2 are the two genes most often found to have a change.
Women with triple negative breast cancer are sometimes offered genetic testing. This is offered even if they do not have a family history of breast cancer. Most breast cancers caused by a change in the BRCA1 gene are triple negative. Your doctor or breast care nurse can explain more about this to you.
If you are worried about breast cancer in your family, talk to your GP or breast specialist. They can refer you to a family history clinic or a genetics clinic.
There are other rare inherited genetic conditions that can increase the risk of breast cancer in women. This includes conditions like neurofibromatosis and Cowden syndrome.
If you have one of these conditions, talk to your GP about whether you may need screening before the NHS breast screening programme’s screening age.
Certain lifestyle factors may slightly increase your breast cancer risk.
The risk of breast cancer is higher in women who are overweight, particularly after the menopause. This is because being overweight may change hormone levels in the body.
Keeping to a healthy weight can help reduce the risk of breast cancer.
Regularly drinking alcohol increases your risk of developing breast cancer. But the risk is small for women who drink within the recommended guidelines.
Smoking may cause a slight increase in breast cancer risk. This seems to be linked with starting smoking at a younger age and smoking for a longer time. We have information on stopping smoking.
Below is a sample of the sources used in our breast cancer information. If you would like more information about the sources we use, please contact us at firstname.lastname@example.org
European Society for Medical Oncology. Primary breast cancer: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. Annals of oncology 26 (supplement 5): v8–v30. 2015.
Morrow M, et al. Chapter 79: malignant tumors of the breast. DeVita, Hellman and Rosenberg’s cancer: principals and practice of oncology (10th edition). Lippincott Williams and Wilkins. 2014.
National Institute for Health and Care Excellence (NICE). Early and locally advanced breast cancer: diagnosis and management. July 2018.
Scottish Intercollegiate Guidelines Network. SIGN 134. Treatment of primary breast cancer: a national clinical guideline. September 2013.
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Rebecca Roylance, Consultant Medical Oncologist.
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