The following are risk factors for breast cancer:
Older age is the main risk factor for most cancers. The chance of getting cancer increases as you get older.
A personal history of breast cancer or benign (noncancer) breast disease
Women with any of the following have an increased risk of breast cancer:
Inherited risk of breast cancer
Women with a family history of breast cancer in a first-degree relative (mother, sister, or daughter) have an increased risk of breast cancer.
Women who have inherited changes in the BRCA1 and BRCA2genes or in certain other genes have a higher risk of breast cancer. The risk of breast cancer caused by inherited gene changes depends on the type of gene mutation, family history of cancer, and other factors.
Having breast tissue that is dense on a mammogram is a factor in breast cancer risk. The level of risk depends on how dense the breast tissue is. Women with very dense breasts have a higher risk of breast cancer than women with low breast density.
Increased breast density is often an inherited trait, but it may also occur in women who have not had children, have a first pregnancy late in life, take postmenopausal hormones, or drink alcohol.
Exposure of breast tissue to estrogen made in the body
Estrogen is a hormone made by the body. It helps the body develop and maintain female sex characteristics. Being exposed to estrogen over a long time may increase the risk of breast cancer. Estrogen levels are highest during the years a woman is menstruating.
A woman's exposure to estrogen is increased in the following ways:
- Early menstruation: Beginning to have menstrual periods at age 11 or younger increases the number of years the breast tissue is exposed to estrogen.
- Starting menopause at a later age: The more years a woman menstruates, the longer her breast tissue is exposed to estrogen.
- Older age at first birth or never having given birth: Because estrogen levels are lower during pregnancy, breast tissue is exposed to more estrogen in women who become pregnant for the first time after age 35 or who never become pregnant.
Taking hormone therapy for symptoms of menopause
Hormones, such as estrogen and progesterone, can be made into a pill form in a laboratory. Estrogen, progestin, or both may be given to replace the estrogen no longer made by the ovaries in postmenopausal women or women who have had their ovaries removed. This is called hormone replacement therapy (HRT) or hormone therapy (HT). Combination HRT/HT is estrogen combined with progestin. This type of HRT/HT increases the risk of breast cancer. Studies show that when women stop taking estrogen combined with progestin, the risk of breast cancer decreases.
Radiation therapy to the breast or chest
Radiation therapy to the chest for the treatment of cancer increases the risk of breast cancer, starting 10 years after treatment. The risk of breast cancer depends on the dose of radiation and the age at which it is given. The risk is highest if radiation treatment was used during puberty, when breasts are forming.
Radiation therapy to treat cancer in one breast does not appear to increase the risk of cancer in the other breast.
For women who have inherited changes in the BRCA1 and BRCA2 genes, exposure to radiation, such as that from chest x-rays, may further increase the risk of breast cancer, especially in women who were x-rayed before 20 years of age.
Obesity increases the risk of breast cancer, especially in postmenopausal women who have not used hormone replacement therapy.
Drinking alcohol increases the risk of breast cancer. The level of risk rises as the amount of alcohol consumed rises.
The best weapon we could have against breast cancer is the ability to stop it occurring in the first place. To do this, we need to know who is most at risk of breast cancer and what we can do to prevent them from developing it.
Our aim is to accurately predict who is at increased risk of breast cancer and enable them to take action with the right interventions – whether that’s lifestyle changes such as diet and exercise, risk-reducing surgery or drugs.
By 2025, we believe we will be able to prevent up to 15% of breast cancer cases.
By 2050, we believe that we will be able to prevent 30% of breast cancer cases.
We’ve pioneered risk and prevention work across research and embedded it in public health and policy campaigns. Now, by building on these strong foundations, we believe we have the potential to drastically reduce the numbers of women developing breast cancer in the future.
Understanding the genetic and lifestyle causes of breast cancer is critical to discovering how to prevent the disease. We need to work out how genetics, such as faults in the BRCA genes, affect the risk of developing breast cancer.
Our researchers are also investigating how a person's genes might work together with non-genetic risk factors (such as age, age at first period, childbirth, and breast density) to collectively increase their overall risk of breast cancer. This knowledge could help to improve current methods of assessing breast cancer risk in people with a family history of the disease.
We don’t yet know enough about what causes male breast cancer and how it differs from breast cancer in women. Our researchers are using samples of male breast tumours donated to our Tissue Bank to study changes to the DNA, to understand how they increase breast cancer risk in men. Ultimately this could help to accurately predict a man’s risk of developing breast cancer.
We are also running one of the world’s largest studies into breast cancer in men to uncover the genetic, lifestyle and environmental factors that increase breast cancer risk in men.
Risk-reducing drugs (chemoprevention) also have a role to play in stopping women developing breast cancer, but with this opportunity comes real challenges. We can’t yet predict which women will respond to these drugs, so our researchers are working hard to figure out who they’re most likely to work for, as well as finding alternatives for those who won’t benefit from existing drugs.
Find out more about the research projects we are funding