Breast cancer is the most common cancer in the UK. The lifetime risk of a woman developing breast cancer is one in eight. The majority of breast cancers (80%) occur in women over the age of 50. Specific causes of breast cancer or why some people get breast cancer and some don't are not known. Research suggests that breast cancer is caused by a combination of many different factors, many of which are beyond our control.
Most breast cancers happen by chance but a small number of people diagnosed with breast cancer (5%) have inherited a fault in one of the known breast cancer genes; BRCA1, BRCA2 or TP53. Our pages on breast cancer in families has more information about this.
What is risk?
Research has shown that some things can increase or decrease the likelihood of getting breast cancer. These are called 'risk factors'. However, as we are all different, risk factors will not affect us all in the same way. One person may have many risk factors and not develop breast cancer, while another may have very few and be diagnosed with it.
Risk measures the chance of something happening. There are a number of ways in which risk is represented. Risk is commonly talked about in two ways – absolute risk and relative risk.
- Absolute risk: the actual chances (odds) of something happening to a person over a period of time. It is not compared to anything, it’s just the likelihood of something occurring. Absolute risk is often reported as a figure such as 1 in 8 (12%).
- Relative risk: the likelihood of something increasing or reducing a particular risk, for example people who smoke compared to non-smokers. Relative risk doesn’t explain your actual risk. Relative risk is often reported as a percentage reduction of the absolute risk.
Sometimes it can be difficult to figure out what a risk means to an individual person in real terms. Cancer Research UK has further information on understanding breast cancer risk.
Risk in the news
News headlines on breast cancer ‘causes’, or ‘breast cancer is linked to…’ stories are frequently reported in the news, but when you look behind the headlines the true story can be very different.
Some news stories about breast cancer risk are based on limited or questionable research, or involve only a small number of people. Sometimes the results are exaggerated or reported in a misleading way and the increase in risk – if proved at all – is very small.
If a breast cancer risk story worries you, finding out more about the research behind the headline can help you decide what that risk means to you. The NHS website looks at the facts behind the headlines.
Main breast cancer risk factors
The three main risk factors for breast cancer are ones we can’t do anything about.
- Increasing age
- Significant family history
Being a woman is the single biggest risk factor for developing breast cancer. Around 55,000 new cases of breast cancer are diagnosed each year in the UK, of which about 400 are in men.
After gender, age is the most significant risk factor for developing breast cancer – the older the person, the higher the risk. Most breast cancers (80%) occur in women over the age of 50. Most men who get breast cancer are over 60.
The table below gives the estimated risk of women developing breast cancer according to age, showing how risk goes up as we get older.
|Risk up to and including age 29||1 in 2,000|
|Risk up to and including age 39||1 in 215|
|Risk up to and including age 49||1 in 50|
|Risk up to and including age 59||1 in 22|
|Risk up to and including age 69||1 in 13|
|Lifetime risk||1 in 8|
So the lifetime risk of developing breast cancer is 1 in 8 (absolute risk) for a woman who lives to be around 84. This also means that 7 out 8 women will not develop breast cancer in their lifetime, and the risk for younger women is much lower.
Significant family history
Because breast cancer is the most common cancer in women in the UK, having someone in your family with breast cancer doesn’t always mean your own risk is increased. For most people, having a relative with breast cancer does not increase their risk.
However, a small number of women and men may have an increased risk of developing breast cancer because they have a significant family history. A family history may be called significant if there are a number of cases of breast and ovarian cancer in the family, or cases at a young age, or male relatives with breast cancer.
Our booklet Breast cancer in families has more information on this.
Other breast cancer risk factors
There are other factors, some of which are listed below, that might slightly increase or decrease the risk of developing breast cancer. Factors increasing risk include:
- previously had breast cancer
- periods starting before the age of 12
- menopause later than average age (52)
- not having children
- first pregnancy at the age of 30 or over
- taking hormone replacement therapy (HRT) – depending on what type you take and how long you take it (the risk reduces over time once you stop)
- taking the oral contraceptive pill for a number of years (the risk reduces over time once you stop)
- a few types of benign (not cancer) breast problems
- dense breasts (seen on mammogram)
- exposure to high levels of radiation
- previously treated with chest radiation for other cancers as a child or young adult
- being overweight, especially after the menopause
- drinking more alcohol than the recommended daily amount (two units for women, three for men)
- smoking (the evidence is inconsistent but suggests this may only be significant for postmenopausal women who start smoking at a young age and continue to smoke for many years).
Factors which may decrease risk include:
- periods starting after the age of 12
- menopause before the age of 45
- having children (especially having the first before the age of 20)
- breastfeeding (for a minimum of five months – this could be one baby or more)
- risk-reducing surgery (only for those who have inherited a faulty gene).
Having one or more risk factors might mean that the likelihood of you developing breast cancer is only slightly greater than if you don’t have these risk factors. It doesn’t mean that you will develop breast cancer and importantly your overall individual risk may still be small. Remember one person may have many risk factors and not develop breast cancer, while another may have very few risk factors and be diagnosed with the disease.
Content last reviewed September 2012; next planned review 2014