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Breast Cancer (cont.)

Breast Cancer Causes: Genes and Hormones

Many women who develop breast cancer have no risk factors other than age and gender.

  • Gender is the biggest risk because breast cancer occurs mostly in women.
  • Age is another critical factor. Breast cancer may occur at any age, though the risk of breast cancer increases with age. The average woman at 30 years of age has one chance in 280 of developing breast cancer in the next 10 years. This chance increases to one in 70 for a woman 40 years of age, and to one in 40 at 50 years of age. A 60-year-old woman has a one in 30 chance of developing breast cancer in the next 10 years.
  • White women are slightly more likely to develop breast cancer than African-American women in the U.S.
  • A woman with a personal history of cancer in one breast has a three- to fourfold greater risk of developing a new cancer in the other breast or in another part of the same breast. This refers to the risk for developing a new tumor and not a recurrence (return) of the first cancer.

Genetic Causes

Family history has long been known to be a risk factor for breast cancer. Both maternal and paternal relatives are important. The risk is highest if the affected relative developed breast cancer at a young age, had cancer in both breasts, or if she is a close relative. First-degree relatives (mother, sister, daughter) are most important in estimating risk. Several second-degree relatives (grandmother, aunt) with breast cancer may also increase risk. Breast cancer in a male increases the risk for all his close female relatives. Having relatives with both breast and ovarian cancer also increases a woman's risk of developing breast cancer.

There is great interest in genes linked to breast cancer. About 5%-10% of breast cancers are believed to be hereditary, as a result of mutations, or changes, in certain genes that are passed along in families.

  • BRCA1 and BRCA2 are abnormal genes that, when inherited, markedly increase the risk of breast cancer to a lifetime risk estimated between 40%-85%. Women with these abnormal genes also have an increased likelihood of developing ovarian cancer. Women who have the BRCA1 gene tend to develop breast cancer at an early age.
  • Testing for these genes is expensive and may not be covered by insurance.
  • The issues around testing are complicated, and women who are interested in testing should discuss their risk factors with their health-care providers.

Hormonal Causes

Hormonal influences play a role in the development of breast cancer.

  • Women who start their periods at an early age (12 or younger) or experience a late menopause (55 or older) have a slightly higher risk of developing breast cancer. Conversely, being older at the time of the first menstrual period and early menopause tend to protect one from breast cancer.
  • Having a child before 30 years of age may provide some protection, and having no children may increase the risk for developing breast cancer.
  • Using oral contraceptive pills means that a woman has a slightly increased risk of breast cancer than women who have never used them. This risk appears to decrease and return to normal with time once the pills are stopped.
  • A large study conducted by the Women's Health Initiative showed an increased risk of breast cancer in postmenopausal women who were on a combination of estrogen and progesterone for several years. Therefore, women who are considering hormone therapy for menopausal symptoms need to discuss the risk versus the benefit with their health-care providers.
Medically Reviewed by a Doctor on 10/3/2014

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