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Breast Cancer Risk Factors

Each year there are more than 276,000 women diagnosed with invasive breast cancer. There are more than 2,600 cases diagnosed in men. Breast cancer is the most frequently diagnosed cancer in women aside from skin cancer. Additionally, there will be more than 48,000 new cases of in situ breast cancer.

Risk Factors

Being female and aging are the two most important risk factors for breast cancer. There is a common misconception among older women that their risk decreases with age when in fact the opposite is true.

Having one or more risk factors does not mean that you will develop breast cancer, in fact most women who have one or more risk factors never develop the disease. Many women with no risk factors develop breast cancer, at this time we don’t know how much these risk factors contribute to the development of breast cancer.

There are different kinds of risk factors, some of these are under our control and can be changed. Risk factors, like age or race, cannot be changed. Other risk factors are linked to the environment. Your risk for breast cancer can change over time, due to factors such as aging or lifestyle changes.

Risk Factors You Cannot Change


Being a woman is the main risk factor for developing breast cancer. The primary reason women develop breast cancer is because the breast cells are constantly exposed to the effects of female hormones, estrogen and progesterone. Breast cancer is also found in men but in much lower numbers than in women.


As you age your risk of developing breast cancer increases. About 1 out of 8 invasive breast cancers are found in women younger than 45, while 2 of 3 invasive breast cancers are found in women age 55 or older.

Genetic Risk Factors

Hereditary breast cancer accounts for 5%-10% of cases, they are thought to be hereditary, resulting from gene mutations inherited from a parent. These can be inherited from either your Mother or your Father.

  • BRCA1 and BRCA2: An inherited mutation in the BRCA1 and BRCA2 genes is the most common hereditary risk factor for developing breast cancer. The risk may be as high as 80% for members of some families with BRCA mutations; they are also at an increased risk for ovarian cancer. These cancers tend to occur in younger women and more often affect both breasts than cancers in women who are not born with one of these gene mutations. These mutations can occur in any racial or ethnic group, however in the United States the BRCA mutations are most often found in Jewish women with Ashkenazi(Eastern Europe) heritage.
  • Genetic testing: Genetic testing can be done to look for mutations in the BRCA1 and BRCA2 genes and is covered by most health insurance plans as long as you meet the criteria for testing. It is important that you speak with a genetic counselor, nurse, or physician who is qualified to explain the results of the tests. Although testing may be helpful in some situations, the pros and cons need to be considered carefully.

Family History of Breast Cancer

Having a first-degree relative (mother, sister, or daughter) with breast cancer almost doubles a woman's risk. Having 2 first-degree relatives triples her risk.

Personal History of Breast Cancer

A woman with a personal history of cancer in one breast has an increased risk of developing a new cancer in the other breast or in another part of the same breast. This is called a second primary cancer and is different from a recurrence of the first cancer.

Race and Ethnicity

Statistics show that white women are slightly more likely to develop breast cancer than African-American women, but show that African-American women are more likely to die from breast cancer.

If we look at the statistics by age, we find that breast cancer is more common in women who are under 45 years of age. It is also shown that Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.

Dense Breast Tissue

Women with denser breast tissue (as seen on a mammogram) have more glandular tissue and less fatty tissue, and have a higher risk of breast cancer. Unfortunately, dense breast tissue can also make it harder for doctors to spot problems on mammograms. If you have dense breasts you should discuss the appropriate imaging studies available to you. The introduction of 3D technology has shown an improvement in imaging studies for women with dense breasts. This technology is available at the Margaret W. Niedland Breast Center, call 561- 263-4414 to schedule an appointment.

Certain Benign Breast Conditions

Women diagnosed with certain benign breast conditions may have an increased risk of breast cancer. Some of these conditions are more closely linked to breast cancer risk than others.

These conditions show excessive growth of cells in the ducts or lobules of the breast tissue and seem to increase a woman’s risk of breast cancer slightly.

  • Usual ductal hyperplasia (without atypia)
  • Complex fibroadenoma
  • Sclerosing adenosis
  • Several papillomas or papillomatosis
  • Radial scar

These conditions also show excessive growth of cells in the ducts or lobules of the breast tissue, with some of cells no longer appearing normal. They have a stronger effect on the risk of developing breast cancer.

  • Atypical ductal hyperplasia (ADH)
  • Atypical lobular hyperplasia (ALH)

Women with a family history of breast cancer and either hyperplasia or atypical hyperplasia have an even higher risk of developing a breast cancer.

Lobular Carcinoma In Situ

Women with lobular carcinoma in situ (LCIS) have a 7 -to 11-fold increased risk of developing cancer in either breast.

Menstrual Periods

Women who started menstruating at an early age (before age 12) and/or went through menopause at a later age (after age 55) causing them to have had more menstrual cycles have a slightly higher risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.

Previous Chest Radiation

For women who had radiation as a child or an adolescent as a treatment for cancer have a significantly increased risk for breast cancer. This varies with the age of the patient when they received the radiation. If chemotherapy was also part of the treatment, it may have stopped ovarian hormone production for some time, lowering the risk. The risk of developing breast cancer from chest radiation is highest if the radiation was given during adolescence, when the breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk.

Diethylstilbestrol (DES) Exposure

The use of DES from the 1940s through the early 1970s for pregnant women to lower their risk of miscarriage has shown a slightly increased risk of developing breast cancer. These women have a slightly increased risk of developing breast cancer. Women whose mothers took DES during pregnancy may also have a slightly higher risk of breast cancer.

Lifestyle-Related Factors

Having Children

Women who do not have children or who had their first child after age 30 have a slightly higher breast cancer risk. Women who became pregnant at an early age or have many children are at a reduced risk for breast cancer. Because pregnancy reduces a woman’s menstrual cycles over her lifetime it is thought to be the reason for the reduced risk.

Recent Oral Contraceptive Use

Studies show that women using oral contraceptives (birth control pills) have a slightly greater risk of breast cancer than women who have never used them. Once the pills are stopped the risk will return to normal over time. If the pills were stopped over ten years ago then there does not appear to be an increased risk. If you use oral contraceptives or are considering using them you should discuss the risks and benefits with your physician.

Hormone Therapy After Menopause

Hormone replacement therapy has been used for many years to relieve symptoms of menopause and help prevent osteoporosis. Estrogen and sometimes progesterone are prescribed. Early studies suggested these hormones might have other health benefits as well, but those benefits have not been found in more recent, better designed studies.

Women who still have a uterus are generally given estrogen and progesterone; this is called combined hormone therapy. Progesterone is used because using estrogen alone increases the risk of uterine cancer. Women who have had a hysterectomy and no longer have a uterus can take estrogen alone.

  • Combined HT: Large studies have shown that the use of combined post-menopausal hormone therapy increases the risk of getting breast cancer and the likelihood that it may be found at a more advanced stage. The increased risk from combined HT appears to apply only to current and recent users. Within five years of stopping hormone therapy a woman’s risk appears to return to that of the general population.

    Bioidentical hormones have been marketed as a safe alternative to estrogen and progesterone. There are very few studies comparing bioidentical hormones to synthetic hormones and no evidence to support that are safer to use. Until studies prove otherwise, the use of these hormones should be assumed to carry the same health risks as any other type of hormone therapy.
  • Estrogen Therapy: The use of estrogen therapy does not appear to increase the risk of developing breast cancer. Some studies have found that long term use of estrogen alone (10 years or longer) increases the risk of breast and ovarian cancer.

Other than the short-term relief of menopausal symptoms, there appears to be little support for the use of either Combined Hormone Therapy or Estrogen Therapy. Aside from the increased risk of breast cancer, combined HT also appears to increase the risk of heart disease, blood clots, and strokes. On the other hand it does lower the risk of colorectal cancer and osteoporosis. We do have ways to prevent and treat osteoporosis and regular colonoscopy screening is the best defense against colorectal cancer. And although estrogen therapy does not seem to increase breast cancer risk, it does increase the risk of stroke.

A decision to use hormone therapy should be made by a woman and her physician after discussing the severity of symptoms from menopause and the possible risks and benefits of therapy. Her other risk factors for heart disease, breast cancer, and osteoporosis should be considered as well. If a decision is made to try hormone therapy for symptoms of menopause, it is usually best to use it at the lowest dose that works for her and for as short a time as possible.


There are some studies that suggest breast-feeding may slightly lower breast cancer risk, especially if it is continued for 1½ to 2 years. This has been a difficult area to study, especially in countries such as the United States, where breast-feeding for this long is uncommon.

The explanation for this possible effect may be that breast-feeding reduces a woman's total number of lifetime menstrual cycles.


Alcohol consumption is clearly linked to an increased risk of developing breast cancer and the risk increases with the amount of alcohol consumed. When compared to non-drinkers, women who consume 1 alcoholic drink a day have a very small increase in risk. Women who have 2 to 5 drinks daily increase their risk about 1½ times the risk of women who drink no alcohol. Excessive alcohol use is also known to increase the risk of developing many other cancers including: mouth, throat, esophagus, and liver. Recommendations are that women have no more than 1 alcoholic drink a day.

Being Overweight or Obese

Being overweight or obese has been found to increase breast cancer risk, especially for post menopausal women. Before menopause your ovaries produce most of your estrogen, and fat tissue produces a small amount of estrogen. When the ovaries stop producing estrogen (after menopause), most of a woman's estrogen comes from fat tissue. By having more fat tissue after menopause your chance of getting breast cancer may be increased because of raised estrogen levels. Women who are overweight also tend to have higher blood insulin levels which have been linked to some cancers, including breast cancer.

The connection between weight and breast cancer risk is complex, risk appears to be increased for women who gained weight as an adult but may not be increased among those who have been overweight since childhood. Excess fat in the waist area may affect risk more than the same amount of fat in the hips and thighs. Researchers believe that fat cells in various parts of the body have subtle differences that may explain this.

It is important maintain a healthy weight throughout your life by balancing your food intake with physical activity and avoiding excessive weight gain.

Physical Activity

There is growing evidence that physical activity in the form of exercise reduces breast cancer risk. The debate is how much exercise is needed. A study from the Women's Health Initiative recommends as little as 1¼ to 2½ hours per week of brisk walking can reduce a woman's risk by 18%. Walking 10 hours a week further reduced the risk. Current recommendations support 30 to 60 minutes of physical activity at least five days a week.

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