Risk Factors for Breast Cancer


About risk factors: Risk factors for Breast Cancer are factors that do not seem to be a direct cause of the disease, but seem to be associated in some way. Having a risk factor for Breast Cancer makes the chances of getting a condition higher but does not always lead to Breast Cancer. Also, the absence of any risk factors or having a protective factor does not necessarily guard you against getting Breast Cancer. For general information and a list of risk factors, see the risk center.

Risk factor list: The list of risk factors mentioned for Breast Cancer in various sources includes:

Protective factors: Certain factors have been mentioned as lowering the risk of Breast Cancer including:

Risk factors discussion: Almost half of the post-menopausal women diagnosed with breast cancer have a BMI 29.16 In one study (the Nurses' Health Study), women gaining more than 20 pounds from age 18 to midlife doubled their risk of breast cancer, compared to women whose weight remained stable.1

Risk is increased with age, such that 80 percent of women with breast cancer are over age 50. Women who have a history of breast cancer in the family, who never have had children, who had a first child after age 30, who began menstruation before age 12 or who complete menopause after age 55 are also at increased risk of breast cancer. Heavy alcohol consumption and obesity have also been shown to increase the risk of breast cancer.2

A family history of breast cancer increases your risk of breast cancer, but it is not necessary to choose more aggressive treatment or more radical surgery just because you have a family member with breast cancer. Research shows that a strong family history of breast cancer does not affect local recurrence rates or overall survival among women who undergo breast-conserving surgery. So family history should not influence your choice of either mastectomy or breast-conserving surgery. 3

Women diagnosed with breast cancer who have a family history of breast cancer are at increased risk of getting breast cancer in their healthy breast. Sometimes these women decide to have the other removed to prevent cancer in the future. Occasionally, women with several close relatives with breast cancer decide to have both their breasts removed as a preventive measure, even if they have never been diagnosed with breast cancer. Removing one or two healthy breasts reduces the risk of future breast cancer, but it does not eliminate the risk completely. The disadvantage is that the surgery will be unnecessary for most women who choose it, because most women who have a breast removed as a preventive measure would never have gotten breast cancer even if the breast (or breasts) were not removed. 3

There are some studies that suggest long term use of HRT (more than 10 years) increases the risk of breast cancer. While there is no definite proof that HRT increases the risk of breast cancer, two new studies that published in the winter of 2000, suggest that combined HRT (estrogen plus progestin) increases the risk of breast cancer more than taking estrogen alone. The National Cancer Institute (NCI) explains that in the first study, the risk for breast cancer among women who had used any form of HRT during the past 4 years was higher than the risk for women who did not use HRT. For women who had taken the combination HRT, however, the risk of breast cancer increased by 8 percent per year; compared to a one- percent increase for women taking estrogen alone. There was no increase in risk among women who had stopped using either type of HRT for 4 years or more. In the second study on HRT, the risk of developing breast cancer increased by 24 percent for every 5 years of use; compared to a 6 percent increase for estrogen-only therapy. Both studies reported that the increased risk of breast cancer associated with either ERT or HRT was higher in thin women. This is an interesting finding, since obesity is a risk factor for breast cancer. 4

Being seriously overweight may be linked to breast cancer among older women and to cancers of the prostate, pancreas, uterus, colon, and ovary. On the other hand, some studies suggest that foods containing fiber and certain nutrients may help protect against some types of cancer.5

Doctors may recommend HRT, using either estrogen alone or estrogen in combination with progesterone, to control symptoms (such as hot flashes and vaginal dryness) that may occur during menopause. Studies have shown that the use of estrogen alone increases the risk of cancer of the uterus. Therefore, most doctors prescribe HRT that includes progesterone along with low doses of estrogen. Progesterone counteracts estrogen's harmful effect on the uterus by preventing overgrowth of the lining of the uterus; this overgrowth is associated with taking estrogen alone. (Estrogen alone may be prescribed for women who have had a hysterectomy, surgery to remove the uterus, and are, therefore, not at risk for cancer of the uterus.) Other studies show an increased risk of breast cancer among women who have used estrogen for a long time; and some research suggests that the risk might be higher among those who have used estrogen and progesterone together.5

Research has shown that the following conditions increase a woman's chances of getting breast cancer:

  • Personal history of breast cancer. Women who have had breast cancer face an increased risk of getting breast cancer in their other breast.

  • Family history. A woman's risk for developing breast cancer increases if her mother, sister, or daughter had breast cancer, especially at a young age.

  • Certain breast changes. Having a diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase a woman's risk for developing cancer.

  • Genetic alterations. Changes in certain genes (BRCA1, BRCA2, and others) increase the risk of breast cancer. In families in which many women have had the disease, gene testing can sometimes show the presence of specific genetic changes that increase the risk of breast cancer. Doctors may suggest ways to try to delay or prevent breast cancer, or to improve the detection of this disease in women who have these changes in their genes. For more information about gene testing, read the "Causes and Prevention" section under "The Promise of Cancer Research."

Other factors associated with an increased risk for breast cancer include:

  • Estrogen. Evidence suggests that the longer a woman is exposed to estrogen (estrogen made by the body, taken as a drug, or delivered by a patch), the more likely she is to develop breast cancer. For example, the risk is somewhat increased among women who began menstruation at an early age (before age 12), experienced menopause late (after age 55), never had children, or took hormone replacement therapy for long periods of time. Each of these factors increases the amount of time a woman's body is exposed to estrogen.

    DES (diethylstilbestrol) is a synthetic form of estrogen that was used between the early 1940s and 1971. Women who took DES during pregnancy to prevent certain complications are at a slightly higher risk for breast cancer. This does not appear to be the case for their daughters who were exposed to DES before birth. However, more studies are needed as these daughters enter the age range when breast cancer is more common.

  • Late childbearing. Women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.

  • Breast density. Breasts that have a high proportion of lobular and ductal tissue appear dense on mammograms. Breast cancers nearly always develop in lobular or ductal tissue (not fatty tissue). That's why cancer is more likely to occur in breasts that have a lot of lobular and ductal tissue (that is, dense tissue) than in breasts with a lot of fatty tissue. In addition, when breasts are dense, it is more difficult for doctors to see abnormal areas on a mammogram.

  • Radiation therapy. Women whose breasts were exposed to radiation during radiation therapy before age 30, especially those who were treated with radiation for Hodgkin's disease, are at an increased risk for developing breast cancer. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.

  • Alcohol. Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol.

Most women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older. Scientists are conducting research into the causes of breast cancer to learn more about risk factors and ways of preventing this disease.6

Some aspects of a woman's lifestyle may affect her chances of developing breast cancer. For example, recent studies suggest that regular exercise may decrease the risk in younger women. Also, some evidence suggests a link between diet and breast cancer. Ongoing studies are looking at ways to prevent breast cancer through changes in diet or with dietary supplements. However, it is not yet known whether specific dietary changes will actually prevent breast cancer. These are active areas of research.

Scientists are trying to learn whether having a miscarriage or an abortion increases the risk of breast cancer. Thus far, studies have produced conflicting results, and this question is still unresolved.6

Risks factors for Breast Cancer: medical news summaries: The following medical news items are relevant to risk factors for Breast Cancer:

1. excerpt from NIDDK _ Statistics Related to Overweight and Obesity: NIDDK
2. excerpt from Breast Cancer: NWHIC
3. excerpt from Early Stage Breast Cancer: NWHIC
4. excerpt from Hormone Replacement Therapy: NWHIC
5. excerpt from What You Need To Know About Cancer - An Overview: NCI
6. excerpt from What You Need To Know About Breast Cancer: NCI

Last revision: April 9, 2003

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