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Breast Cancer: Overview and Risk Factors

Breast cancer is the most common cancer of women and the second most common cause of cancer death in women. In the United States, one in nine women will be diagnosed with invasive breast cancer over a lifetime.

The development of breast cancer has been associated with increased levels of estrogens–female sex hormones–in the body.  These states include long–term use of menopausal hormone “replacement” therapy and uninterrupted menstrual cycles, including early onset of menstrual periods or late onset of menopause. Food choices and body fat accumulation can also affect the amount of estrogen in a woman’s bloodstream.

Symptoms may include a breast lump; thickening, dimpling, or redness of the skin of the breast; or bloody nipple discharge. Breast pain or tenderness is usually not associated with cancer. In many cases, the only sign of disease is an abnormal mammogram.

Breast cancer does occur in men, although it is relatively rare. For men, the incidence is about 1 percent of the rate in women.

There is an 85 percent five–year survival rate. Early diagnosis and treatment is important because breast cancers can become invasive and spread throughout the body.

Risk Factors 

  • Age: Incidence increases with age.
  • Family history: Having a first–degree relative with breast cancer increases the risk.
  • Genetics: Researchers have discovered two genes, named BRCA1 and BRCA2, which are related to breast cancer. Mutations of these genes significantly increase the risk of cancer.
  • Increased estrogen states: These include long–term use of menopausal hormone “replacement” therapy, uninterrupted menstrual cycles (including early onset of menstrual periods, late onset of menopause, older age at first birth, and nulliparity (having never given birth). In a clinical trial with 7,705 women, those with the highest blood estrogen levels had double the risk for invasive breast cancer.

    The Women's Health Initiative study showed a higher risk of breast cancer among women taking estrogen and progesterone hormone “replacement” therapy for approximately five years, in comparison with those who used a placebo.
  • Radiation exposure
  • Shorter duration of breast–feeding: Several studies show protective benefits of breast–feeding. A multinational study of nearly 150,000 women showed a decreased risk of 4.3 percent for each year of breast–feeding and 7 percent for each pregnancy.
  • Obesity
  • History of ovarian cancer
  • Elevated blood glucose: The Nurses’ Health Study found that postmenopausal women with diabetes had a slightly greater risk for breast cancer. Other studies have found greater risk for breast cancer in nondiabetic women with higher levels of fasting glucose.
  • Race: Breast cancer incidence, aggressiveness, and mortality are higher in African–American women, compared with whites.
  • Other: Moderate sunlight exposure and physical activity are associated with a reduced risk. Despite common beliefs, most studies have not shown increased risk from silicone breast implants, electromagnetic fields, electric blankets, hair dyes, or organochlorines. 


Breast Cancer: Diagnosis and Treatment >>