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Breast Cancer Causes & Risks

Breast Cancer Causes & Risk Factors

Medical researchers do not fully understand what causes breast cancer. Like other cancers, it’s a condition in which particular cells grow in an abnormal and uncontrolled way. Eventually, these cancerous cells can invade into nearby healthy breast tissue and eventually find their way out into other parts of the body.

Scientists have isolated some genes that, if mutated, seem to contribute to the development of breast cancer. These are breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2). These genes are found in up to 10 percent of people with breast cancer. However, even in the presence of these mutated genes, experts don’t know what causes the additional biochemical events that are required in order for breast cancer to develop.

There may be certain aspects of your medical history or lifestyle that increase your risk of breast cancer. Below are some of those risk factors that may lead to breast cancer. If you have concerns about any of them, talk to your doctor.

Unavoidable Risk Factors


Women are diagnosed with breast cancer 100 times more often than men. This is believed to be related to the female sex hormones.  Specifically, estrogen and progesterone are the hormones most likely related to breast cancer. In some breast cancers, these hormones act as promoters of cell growth and division. Cancer risk may increase since breast cells are exposed to these potential growth-drivers during the female menstrual cycle.


According to the American Cancer Society, more than two-thirds of invasive breast cancers are found in women age 55 and older. Only one-eighth is found in women under age 45. Male breast cancer most often strikes those between age 60 and 70.

Family History

Women have a higher risk of breast cancer if they have a first-degree blood relative (such as a mother, sister, or daughter) who has been diagnosed with the disease. Two first-degree relatives increase a woman’s risk by five times.


According to the Memorial Sloan Kettering Cancer Center, the genetic mutations of BRCA1 and BRCA2 genes are, by far, the most common known causes of inherited breast cancer. They account for almost the entire 10 percent of hereditary cases. BRCA mutations may increase the risk of developing breast cancer to as high as 85 percent by age 70 in some families.

In the U.S., women of Eastern European Ashkenazi Jewish backgrounds have been found to have disproportionately high occurrence of BRCA mutations. While BRCA1 mutations appear to mainly affect the risk of breast cancer in women, BCR2 gene mutations increase the breast cancer risk in both women and men.  Other genes that are implicated in hereditary breast cancers, though rare, include ATM, p53, CHEK2, PTEN, and CDH1.

Women of European background are most likely to be diagnosed with breast cancer. However, African American women are more likely to die from the disease. Breast cancer is also the No. 1 cause of cancer death in Hispanic women.

Personal Factors

Some physical characteristics have shown to increase a woman’s risk for breast cancer. These include:

  • periods that begin before age 12 (early menses)
  • going through menopause after 55 (also called "delayed menopause")
  • having dense breasts

Lifestyle Risk Factors

Certain lifestyle factors can also contribute to a person’s risk of breast cancer. According to the American Cancer Society, these include:

  • obesity or being overweight
  • high alcohol consumption
  • not having children
  • having your first child after age 35
  • taking birth control pills
  • using hormone replacement therapy

Risk Factors For Men

Though women are more likely to be diagnosed with breast cancer, men are also at risk. Certain risk factors for men include:

  • high levels of estrogen (due to cirrhosis of the liver, for example) or estrogen-related drugs (such as some of those used for prostate cancer)
  • exposure to radiation
  • age over 60
  • high alcohol consumption
  • obesity
  • Klinefelter’s syndrome (a genetic chromosomal abnormality)
  • inherited gene mutations (i.e. BCR2 as noted above)
  • family history of breast cancer


Talk to your doctor if you are concerned about any of these risk factors. You may be able to make certain lifestyle adjustments to lower your risk. Discuss your medical and family history with your doctor to make sure they have all the information necessary to assess your risk.

Content licensed from:

Written by: the Healthline Editorial Team
Medically reviewed on: Sep 02, 2014: Kenneth R. Hirsch, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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