Common Risk Factors

There are a number of risk factors that impact the probability of developing breast cancer, including:

Age
Aside from being female, age is the single greatest risk for developing breast cancer.  Most breast cancers occur in women older than age 50.

 
Family History
About 20-30% of women diagnosed with breast cancer have a family history of the disease.  If you have a first degree relative – a parent, sibling or child – who has had breast cancer, your risk of getting it approximately doubles.

 
Gene Mutations and Predisposition
Researchers have identified specific gene mutations (abnormal changes) that are linked with increased breast cancer risk.  The most common of these, BRCA1 and BRCA2, account for approximately 5-10% of all breast cancers.  The risk of developing breast cancer for women with BRCA1 and BRCA2 mutations significantly increased – as high as 80% during their lifetime.  Everyone inherits these two genes, but the problem arises when they are mutated.  Mutations can often cause breast cancer to occur at a younger age, before menopause, or in both breasts.  BRCA1 and BRCA2 mutations are also associated with a higher risk of ovarian cancer.  Men can also carry these genetic mutations, so the genes can be passed down on the father’s side of the family.

Blood tests can determine if you are a BRCA1 or BRCA2 mutation carrier.   You should only have these tests after you have had genetic counseling.  Counseling not only helps you determine whether the tests are needed, it also helps you decide on appropriate steps to lower your risk of developing breast cancer.

Researchers have identified, and are continuing to identify, other genetic mutations linked to breast cancer.  These mutations are more rare and often do not increase a woman's risk of developing breast cancer as much as BRCA1 and BRCA2.  They include ATM, p53, CHEK2, PTEN, and CDH1.

 
Hormone Exposure and Hormone Replacement Therapy
From the time a woman reaches puberty, hormones play a key role in her life.  Estrogen and progesterone control the development of secondary sex characteristics, menstrual cycles, pregnancy and menopause.  They can also play a role in the development of breast cancer.

• Menstruation: Women who begin menstruating early (before age 12) or go through menopause late (after age 55) have a slightly higher rate of breast cancer.
• Pregnancy: Women who have their first pregnancy after age 35, or who never have a full-term pregnancy, have a slightly higher rate of breast cancer.
• Hormone Replacement Therapy (HRT): Recent use of hormones (within five years) or long term use of HRT (several years or more) is linked to an increased risk of breast cancer.  HRT is a complex and controversial issue.  The decision whether to take hormones during and after menopause depends on many factors.  Every woman who is considering HRT should be aware of the potential risks and discuss her options with her doctor.

"Lifestyle Factors": Diet, weight, exercise and alcohol
We can't control our age or our family history, but we do have some influence over our lifestyle – the things that we eat and drink, our weight, and the amount of exercise we get.  Research has shown that these factors may contribute to the development of some breast cancers:

• Weight: Recent studies have demonstrated that postmenopausal women who are obese (Body Mass Index or BMI of more than 30) have an increased risk of breast cancer.  The increased risk for obese women is largely a result of the fact that after menopause most of a woman's estrogen comes from fat tissue.  More fat tissue means higher estrogen levels, which can lead to an increased risk of breast cancer.
• Alcohol: Women who consume one alcoholic drink a day have a very small increased risk of breast cancer.  That risk goes up with the amount of alcohol consumed.  Most experts recommend that women limit their alcohol consumption to no more than one drink a day.
• Diet: Researchers have known for many years that the incidence of breast cancer is lower in countries where women consume a low fat diet, but studies that have looked into the link between specific diets or foods and breast cancer have produced inconclusive or conflicting results.  Most experts agree that significant health benefits result from eating a diet rich in fruits and vegetables and lower in fat and animal products, and more than just in terms of cancer risks.
• Exercise: A growing body of evidence supports exercise for reducing breast cancer risk.  The Women's Health Initiative showed that brisk walking for as little as 1.25 to 2.5 hours a week reduced breast cancer risk by 18%.  Many experts recommend exercising a minimum of 30 minutes a day.

Your Breasts
Every woman's breasts are unique.  Your breast history can influence your risk of developing breast cancer.  Women with dense breast tissue – which is composed of more glandular tissue and less fatty tissue – are at higher risk for breast cancer.  Radiologists have more trouble spotting problems on mammograms of dense breast tissue.

Many women develop benign breast conditions during their lives.  Some of these are associated with a higher risk of breast cancer while others are not:

• Non-proliferative lesions are those that do not involve an overgrowth of breast tissues.  They include fibrocystic disease, mild hyperplasia, adenosis, ductal ectasia, benign phyllodes tumors, mastitis and a number of other benign tumors.
• Proliferative lesions without atypia: These conditions are characterized by excessive growth of cells in the ducts or lobules and are linked to a slight increase in breast cancer risk.  They include ductal hyperplasia (without atypia), complex fibroadenoma, sclerosing adenoma and several other benign tumors.
• Proliferative lesions with atypia: In these conditions, excessive growth of the cells in the ducts or lobules make the cells appear abnormal when they are examined under the microscope.  These are considered to be precursors of breast cancer and raise a woman's risk by 4 to 5 times.  The most common conditions in this category are atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH).
• Lobular carcinoma in situ: Women with this condition have a higher risk of developing invasive breast cancer in either breast by 7 to 11 times.