Risk factors for breast cancer

There are many risk factors for breast cancer, not one single cause. It’s a combination of our genes, environment and lifestyle.

Some risks we can’t control, such as our gender, age and medical history. Other risks we can manage or reduce through changes such as diet and exercise.

One person may have many risk factors and not develop breast cancer; another may have very few and be diagnosed with it.

Age

As with many other diseases, your risk of breast cancer increases as you get older.

It can happen in younger women, but most breast cancers occur after menopause. About 75% of breast cancer cases are in women aged 50 years and over.

Alcohol

Regularly drinking alcohol can increase your risk of breast cancer. Reducing your alcohol intake can reduce the risk but there is no known ‘safe’ level.

Alcohol may:

• help cancer-causing molecules to enter cells or damage cell DNA
• increase levels of the hormone oestrogen.

History of breast cancer or benign breast disease

People who have had invasive (early) breast cancer have a higher risk of developing cancer in their other breast.

Non-invasive breast conditions are linked to an increased risk of breast cancer. These include ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).

Some benign (non-cancerous) breast conditions can also increase your risk:

• atypical hyperplasia
• lobular neoplasia.

Most benign breast conditions do not increase the risk of breast cancer.

Breast density 

Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. ‘Dense breasts’ mean a mammogram shows there is more fibrous and glandular tissue, and less fatty tissue.

People with very dense breasts have an increased risk of developing breast cancer.

Read about Breast density and breast cancer risk.

Family history and genetics

Around 5 to 10% of breast cancers are in people who inherit a gene fault or ‘mutation’ from a parent. Your risk may also be higher if close relatives have had breast cancer or some other cancers.

Genetic testing can show if you have inherited an abnormal gene. Talk to your GP if you are concerned about your risk.

Read about Breast cancer risk in families.

Read about Genetic mutations and breast cancer risk.

Menopausal hormone therapy (MHT)/hormone replacement therapy (HRT)

Studies show taking combined hormone replacement therapy (oestrogen and progesterone together) for 5 years or more gives you a higher risk of breast cancer.

These studies also show that this risk reduces over time once you stop.

Menstrual history

Women whose periods started before they were 12 years of age have a higher risk of breast cancer later in life.

The same is true for women who go through menopause when they're older than 55.

Oral contraceptive pills

A number of studies suggest the risk is increased while you are taking oral contraception. This increase can remain for up to 10 years after you stop taking the pill.

For most young women in their 20s and 30s the increase is small. It may be greater for older women and those with other strong risk factors.

Pregnancy and breastfeeding

Women have a higher risk of breast cancer if they:

• have never had a full-term pregnancy
• have their first child after the age of 30 years.

Your risk is also higher if you don't breastfeed.

Radiation before age 30

Radiation to your chest to treat another cancer (not breast cancer), such as Hodgkin's disease or non-Hodgkin's lymphoma, may increase your risk of breast cancer. 

Sex

Being a woman is the single biggest risk factor for developing breast cancer.  It’s the most common cancer affecting women in Australia. One in 7 women will be diagnosed with breast cancer in their lifetime. In men, this figure is 1 in 556. 

Smoking

The link between smoking and breast cancer is unclear, but toxins from cigarettes have been found in breast cells.

Smoking can increase complications from breast cancer treatment, including:

• damage to the lungs from radiation therapy
• difficulty healing wounds after surgery and breast reconstruction
• higher risk of blood clots when taking hormone-blocking therapy medicines such as Tamoxifen.

Choosing not to smoke is always a smart health decision. If you smoke and drink, your risk for some cancers increases even more.

Weight and obesity

People who are overweight or obese have a higher risk of breast cancer than people who maintain a healthy weight. This is especially true after menopause.

After a breast cancer diagnosis, being overweight can increase the risk of breast cancer coming back (recurrence).  More fatty tissue means higher oestrogen levels, which may increase the risk.