A large number of risk factors for breast cancer, or attributes increasing your odds of developing breast cancer, have been identified. It is important to recognise that these do not illustrate the complete picture; the vast majority of people who have even multiple risk factors will never go on to develop cancer.
Some risk factors arise from elements that you cannot change, for example your gender, your age, or your family history. Other, “modifiable” risk factors, such as diet and exercise patterns, can be changed to decrease your risk.
The most important risk factors for breast cancer are being female and increasing age.
Non-modifiable risk factors
It may sound obvious, but being female is the single greatest risk factor for developing breast cancer. Whilst breast cancer can develop in men, it is roughly 100 times more common in women, likely due to hormonal differences that promote breast cancer growth.
Breast cancer, like most cancers, increases in prevalence with age. Almost two thirds of invasive breast cancers are found in women aged over 55 years old.
The average risk for a woman in her 30s is approximately 1 in 250, whereas for a woman in her 70s this increases to roughly 1 in 30.
Some breast cancers, about 5-10%, are thought to derive from gene mutations inherited from a parent.
The most common of the identified gene mutations are BRCA1 and BRCA2. Normally, these genes protect against cancer by making proteins that prevent abnormal cell growth. A defective copy of these genes increases your risk of developing breast cancer at some point in your life.
Often, breast cancers occurring in younger women or occurring in both breasts are associated with these mutations. The lifetime risk associated with the BRCA1 mutation is generally 55-65%, although it has been known to be higher in some families. With BRCA2, the lifetime risk tends to be slightly lower at 45%.
These mutations increase the risk of developing some other cancers, particularly ovarian cancer.
BRCA1 and BRCA2 mutations are very common in Jewish people of Ashkenazi (Eastern European) decent, although they can be found in anyone.
Many other gene variants exist that increase the risk of breast cancer (such as the TP53 or CHEK2 genes); these are much rarer, and do not have the same marked increase in breast cancer risk as BRCA mutations.
Genetic testing can be undertaken to look for BRCA mutations, as well as some other known mutations linked with breast cancer; however, the pros and cons of testing must be carefully considered and discussed.
Women presenting with breast cancer less then 30 years of age, women of Jewish background and women with specific types of breast cancer eg- women less then 35 years with Her 2 positive breast cancer or women less then 45 years with ‘triple negative’ ( ER/PR/Her 2 negative) will be offered a funded genetic test.
Women who have a strong family history of multiple relatives with breast cancer or a family history of male breast cancer or ovarian cancer , a family member with breast cancer in both breasts or a family member with young age of onset of breast cancer ( < 40 years old) may be referred to a familial cancer clinic for genetic counselling and or testing.
People with a strong family history of breast cancer have an increased risk of developing it themselves, independent of identified genetic mutations.
A strong family history refers to one or multiple first-degree relatives (mother, sister or daughter), doubling and tripling the lifetime risk respectively. Women whose male relatives have had breast cancer also have a markedly increase risk.
Overall, however, over 85% of women diagnosed with breast cancer do not have a family history of the disease. As ovarian cancer can be associated with genetic mutations such as BRCA1 and BRCA2, a family history of ovarian cancer is also relevant in assessing risk.
Past history of breast cancer
If you have had breast cancer in the past, the risk of developing a new cancer is increased 2- to 6-fold. This is not the same as a recurrence of the first cancer, and can occur in the other breast or a different part of the same breast.
Other breast conditions
Other pre-cancerous or pre-invasive breast conditions, such as ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS), atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH), can be associated with a notable increase in lifetime risk.
Increased breast density on mammogram is also emerging as a strong risk factor. Women whose breasts show the highest degree of breast density have a 4- to 6-fold increase in their lifetime risk of developing cancer.
Women who begin having periods earlier (before age 12) or who have their menopause later (after age 55) have a moderately increased risk of developing breast cancer. This arises due to a greater number of menstrual cycles, and greater lifetime exposure to the hormones oestrogen and progesterone.
Modifiable risk factors
Children and breastfeeding
Women who have not had a full-term pregnancy, or who had their first child after the age of 30, have a higher risk of breast cancer compared to women who had children before age 30.
Breastfeeding, particularly if for 12 months or longer, can lower breast cancer risk.
Overweight or obesity
Being overweight or obese can be a risk factor for breast cancer, predominantly amongst post-menopausal women.
Before menopause, the majority of your oestrogen is produced by the ovaries. Following menopause, when the ovaries shut down, oestrogen is produced by fat tissue instead, and so a greater amount of fat tissue can increase oestrogen exposure.
There is an association between alcohol consumption and the risk of developing breast cancer, amongst many other cancers.
For women who drink one standard drink per day, the risk increase is minimal. Women who drink two to five standard drinks per day have roughly 1½ times the risk of women who do not consume alcohol.
The oral contraceptive pill has been linked with a slight increase in the risk of breast cancer; however, this risk returns to normal in women who stopped using birth control pills more than 10 years ago. Women should discuss their other risk factors for breast cancer with their doctor when thinking about using birth control.
Hormone replacement therapy (HRT)
Use of hormone replacement therapy (HRT) is associated with a small increase in the risk of breast cancer. This should be discussed with your doctor when considering commencement of HRT.
Patients who have undergone ‘mantle’ radiotherapy to treat lymphoma are at increased risk of developing breast cancer and should be monitored with annual breast examination and breast MRI.
Factors that do not increase your risk
Abortions or pregnancy termination
Underarm antiperspirants or deodorants
Silicone breast implants