Breast cancer risk

Breast cancer is the most common form of cancer to affect New Zealand women, but the cause of the disease is not yet known.

On this page we explore the known risks and some recently identified possible risks. We also look at steps you can take to lower your chances of getting breast cancer.  


There are some factors that increase your risk of getting breast cancer. These include:

  • being a woman
  • getting older
  • having several close relatives, such as a mother, sister, or daughter, who have been diagnosed with the disease
  • having had breast cancer before
  • certain conditions such as atypical ductal hyperplasia or lobular carcinoma in situ

If you have these risk factors, it does not mean you will get breast cancer, but you may be more likely to than some other women. However, most women who get breast cancer have no known risk factors, other than getting older.

Some women may have inherited a "breast cancer gene". Around five per cent of breast cancers are thought to be caused by an inherited gene fault. Two gene mutations have been found to be associated with breast cancer - BRCA1 and BRCA2 and both men and women are more likely to get breast cancer if they have these genes. Screening for these genes is possible if you have a strong family history of breast cancer.

Note: Genetic Health Service NZ (GHSNZ) has recently made changes to the way in which people who have a family history of breast cancer are assessed. These changes have come about following international changes to both risk assessment software and the revised criteria for genetic testing. The updated assessment process has resulted in a lowering of the estimated risk and revised surveillance recommendations for some families. If your family was seen by GHSNZ prior to November 2016, you may wish to discuss the possibility of a re-referral to the Genetic Service with your doctor. (July 2017)

More studies are being done into possible risk factors for breast cancer. Work is still underway in many of these areas, but so far the following have been identified as possible risk factors:

  • early menstruation (before age 11). This increases the amount of time the breast tissue has been exposed to the hormone oestrogen. Prolonged exposure to oestrogen may increase the risk of breast cancer
  • late menopause, which prolongs the exposure of breast tissue to oestrogen
  • late pregnancy or no pregnancy. Oestrogen levels are lower during pregnancy so women who have never been pregnant or became pregnant after the age of 35 may have been exposed to higher oestrogen levels than other women
  • use of combined Hormone Replacement Therapy (HRT) (oestrogen and progesterone) for longer than five years
  • obesity may increase the risk of breast cancer in post menopausal women
  • alcohol may change hormone levels in your body and therefore increase your risk of breast cancer.

Can I prevent breast cancer?

There's no way to prevent breast cancer, but you can take steps to try and decrease your chances of contracting this disease.

Preventative steps that may decrease your risk of breast cancer, include:

  • Exercising for four or more hours a week may decrease hormone levels and help to lower breast cancer risk.
  • Maintaining a  healthy weight.
  • Lowering eostrogen levels - breast feeding as long as possible, because oestrogen levels are lower while breast feeding.
  • Drugs known as aromatase inhibitors lower the risk of new breast cancers occuring in post menopausal women with a history of breast cancer.

Find out more

Visit this link on the Cancer Australia website for more information about risk factors. Read this assessment of breast cancer risk factors put together by the Australian organisation National Breast and Ovarian Cancer Centre (NBOCC) (note NBOCC is now part of Cancer Australia).

You may like to read this article from Britain's Daily Mail which has a comprehensive round-up of the various risks usually associated with of breast cancer.