What causes breast cancer

The causes of breast cancer are not fully understood, but some factors that are known to increase the risk.

Being a woman

Being a woman is the main risk factor for breast cancer. Women are 100 times more likely to develop breast cancer than men.

Growing older

Age is the next biggest risk factor in developing breast cancer. Around 75% of all breast cancers occur in women over the age of 50. Current research shows that breast cancer screening is most effective in detecting early breast cancer in women aged 50-74 years.

Family history

Having a first-degree relative (parent, sibling or child) who developed breast cancer before the age of 50 increases a woman’s risk of developing breast cancer.
However, 9 out of 10 women who develop breast cancer do not have a family history of breast cancer.

If you are concerned about your family history of breast cancer, you may wish to go to the Cancer Australia website for more information. There is also a breast cancer risk calculator on the website that can calculate a woman’s breast cancer risk (if she has not already been diagnosed with breast or ovarian cancer).

Being overweight

Overweight women are at an increased risk of developing breast cancer, particularly after menopause. The level of risk increases with increasing body weight.

Alcohol

Having more than two standard drinks per day increases a woman’s risk of developing breast cancer. This risk increases with each additional standard alcoholic drink.

Hormone replacement therapy (HRT)

Use of combination hormone replacement therapy by postmenopausal women for five or more years is associated with a small increased risk of breast cancer.
An individual woman’s level of risk in relation to HRT will vary according to her circumstances and medical history. Women who are considering starting or who are taking HRT should always discuss their risks and options with their doctor.

Oral contraceptive

Women who use oral contraceptives (the Pill) have a small increase risk of breast cancer while using combined oral contraceptives and in the 10 years after stopping.

Having a child late in age or not having any children

Women who have their first child at an early age have a lower risk of breast cancer. Women who never have any children or who have a child later in life have a slightly higher risk of developing the disease.

Age at puberty or menopause

Starting menstruation before the age of 12 and experiencing late menopause (age 55 or after) are both associated with a slightly higher breast cancer risk.