Browser does not support script.
Skip to main content
Find out how we produce our information|
The causes of breast cancer are unknown. But certain things called risk factors| can affect a woman’s chances of getting breast cancer. Having risk factors doesn’t necessarily mean you will get breast cancer. Some women get it while others (with the same risk factors) don’t.
Even though the exact causes of breast cancer aren’t fully known, it’s likely to be caused by a combination of different risk factors rather than just one.
This page is for women with breast cancer. We also have information about breast cancer in men|.
Here we explain some of the known breast cancer risk factors:
The risk of breast cancer increases with age. It’s rare in women under 35, and 8 out of 10 breast cancers (80%) occur in women aged 50 or over.
Women who’ve had breast cancer or other breast conditions in the past may be at a higher risk of developing breast cancer. This includes women who have previously had:
Exposure to the hormones oestrogen and progesterone for long, uninterrupted periods can affect your breast cancer risk. Factors that increase this risk include:
The following lifestyle factors may slightly increase your risk of breast cancer:
Drinking more than two units of alcohol a day over many years can damage your liver. This increases your breast cancer risk because the liver helps to control oestrogen levels.
After the menopause, body fat is the main source of oestrogen. So if you’re overweight, the level of oestrogen in your body may be high, increasing your breast cancer risk.
Smoking heavily over many years, especially if you started smoking at a young age, increases your risk.
Only 5–10% of breast cancers are thought to be linked to an inherited breast cancer gene. Our genes store the biological information we inherit from our parents. The genes most commonly linked to an increased risk of breast cancer in families are BRCA1 and BRCA2. Other genes have been identified, but they only slightly increase the risk. If you have one relative who was diagnosed with breast cancer at an older age, it’s not likely that the cancer is due to an inherited breast cancer gene.
A genetic change (mutation) that increases the risk of breast cancer is only likely to be present in a family if:
Close relatives, sometimes called your first degree relatives, are parents, children, sisters and brothers.
Our section on cancer genetics| explains more about family history and assessing risk.
Women aged 40–50 may be able to have regular screening before they reach 50, depending on their degree of risk.
We have more information about breast screening in women under 50 with a family history of breast cancer|.
We have an online interactive tool called OPERA| (Online Personal Education and Risk Assessment), which gives personalised information about inherited breast cancer risk. OPERA is based on guidance on familial breast and ovarian cancer from the National Institute for Health and Clinical Excellence (NICE). NICE is an independent body that currently gives guidance on NHS services in England and Wales.
OPERA asks you a number of questions about your personal and family history of breast and ovarian cancer. It then gives a tailored personal assessment based on your answers.
The program also gives details of websites, helpful information and further support. OPERA isn’t supposed to take the place of professional genetic counselling services, so if you’re concerned about genetic risk, you should still consult your GP. You may want to take along a copy of your personal assessment when you see them.
Content last reviewed: 1 August 2011
Next planned review: 2013
For answers, support or just a chat, call the Macmillan Support Line free (Monday to Friday, 9am-8pm)
If you have any questions about cancer, need support or just want someone to talk to, ask Macmillan.
OPERA is our Online Personal Education and Risk Assessment tool, which might help if you are worried about your risk of breast or ovarian cancer.
If you have any questions about Macmillan we would love to hear from you| .
You can also follow us| on Facebook, Twitter, Flickr or YouTube.
© Macmillan Cancer Support 2013
what are these?|