Breast cancer is the most common cancer affecting women in NSW and ranks equally with lung cancer as one of the two leading causes of death from cancer amongst NSW women. In 2006, 27.2% of all cancers diagnosed in women in NSW were breast cancer and around one in eleven women will develop breast cancer by the age of 75 years and one in nine by the age of 85 years.
 
Breast cancer is a collection of cells in the breast tissue that grow in an uncontrolled manner. The cancer can be non-invasive, meaning that it stays within the breast, or malignant, meaning it is able to spread.
 
There are several types of breast cancer depending on the location of the cancer within the breast tissue. Breast cancer is usually a slow growing cancer. If the disease spreads it can invade the lymph nodes under the armpit, and can then invade other tissues such as the bones and lungs.

There is no single cause for breast cancer. However, there are factors which have been identified that may be associated with an increased risk of developing breast cancer.

Risk Factors

Age and being female are the biggest risk factors for developing breast cancer.
 
During 2006 in NSW females comprised over 99% of new breast cancer cases and, of these, over three-quarters of breast cancer diagnoses and 86.7% of deaths were in women 50 years and over.

A number of other factors influence a woman’s risk of breast cancer more moderately.

Increased risk

• not having children or having them after the age of 30 years
• early onset of menarche
• late onset of menopause
• no or limited breastfeeding
• increased body weight (post-menopausal breast cancer)
• alcohol consumption 
• family history

Decreased risk

• bearing children
• early pregnancy
• late onset of menarche
• early onset of menopause
• breastfeeding
• higher levels of physical activity

Family History
 
A woman's risk of breast cancer is two or more times greater if she has a first degree relative (mother, sister or daughter) who developed the disease before the age of 50, and the younger the relative was when she developed breast cancer the greater the risk.
 
Many women tend to overemphasise family history as a risk factor when in fact eight out of nine women who develop breast cancer do not have a mother, sister or daughter who has had breast cancer.
 
BreastScreen NSW recommends that women with a strong family history of breast cancer discuss their circumstances with their doctor.