Risk factors for breast cancer

Each year, about 50,000 women are diagnosed with breast cancer in the UK. It is more common in women who are aged 50 and over, but it can also affect younger women. Improvements in treatment mean more women are surviving breast cancer.

The exact cause of breast cancer is unknown. But certain things called risk factors can increase your chance of developing it. Having one or more risk factors doesn’t mean you will definitely get cancer. Equally, if you don’t have any risk factors, it doesn’t mean you won’t get breast cancer.

Some risk factors for breast cancer include:

  • getting older
  • having had breast cancer or some other breast conditions before
  • lifestyle factors, for example smoking or drinking alcohol
  • a family history of breast cancer, or related cancers such as ovarian cancer.

Breast cancer is likely to be caused by a combination of different risk factors, rather than just one.

Age

The strongest risk factor for breast cancer is increasing age. About 8 out of 10 (80%) women diagnosed are over the age of 50.


Breast cancer and some breast conditions

Your risk is increased if you have had breast cancer before. This includes ductal carcinoma in situ. Having the following breast conditions can also increase your risk:

  • lobular carcinoma in situ (LCIS)
  • atypical ductal hyperplasia – there are slightly abnormal cells in the milk ducts in a small area of the breast
  • dense breast tissue – when the breast is mostly made up of glandular and connective tissue and has very little fatty tissue.


Radiotherapy to the chest at a young age

Women who have had radiotherapy to the chest at an early age (for example to treat Hodgkin lymphoma) have an increased risk of breast cancer.


Hormonal factors

The female hormones oestrogen and progesterone can affect your breast cancer risk. Factors that can increase your risk include:

  • Taking hormone replacement therapy (HRT) – particularly if you are taking combined HRT (oestrogen and progesterone). When you stop HRT, your risk reduces again.
  • Not having children.
  • Having children 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 50).
  • Taking the contraceptive pill, although the risk reduces if you stop taking it.


Lifestyle factors

The following lifestyle factors may slightly increase your breast cancer risk:

Alcohol

Drinking alcohol increases your risk of developing breast cancer. But the risk is small for women who drink within the recommended guidelines.

Being overweight

The risk of breast cancer is higher in women who are overweight, particularly after the menopause. This is because it may change hormone levels in the body.

Smoking

Smoking may cause a slight increase in breast cancer risk. The younger you are when you start smoking and the longer you smoke for, the greater the risk.

Family history and risk

Most women who get breast cancer don’t have a family history of it. 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 greater 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.

Less than 1 in 10 breast cancers 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 change in them.