Causes & Risk Factors

Medical scientists do not fully understand what causes breast cancer. Like other cancers, it is marked by a rapid production of some cells that amass into a tumor. 

Scientists have isolated some genes that, if mutated, seem to cause breast cancer: breast cancer gene 1 (BRCA1) and breast cancer gene 2 (BRCA2). These genes comprise up to 10 percent of breast cancer patients. However, experts don’t know what makes up the biochemical cascade that causes changes in a woman’s genes.

Here are some other risk factors that may lead to breast cancer:

Unavoidable Risk Factors


Women acquire breast cancer 100 times more often than men because of their hormones, specifically estrogen and progesterone. The exposure of breast cells in a woman to these growth-drivers accounts for the huge difference.


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.


The genetic mutations of BRCA1 and BRCA2 genes are, by far, the most prevalent causes of inherited breast cancer. They account for almost the entire 10 percent of hereditary cases. BRCA mutations may spike the risk to 80 percent in some families. In the U.S., women of Eastern European Jewish background have been found to have disproportionately high BRCA mutations. Other genes that are implicated in hereditary breast cancer, 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
  • Going through menopause after 55 (also called "delayed menopause")
  • Having dense breasts

Lifestyle Factors

Risk Factors For Men

  • High levels of estrogen (due to cirrhosis of the liver, for example) or estrogen-related drugs (such as for prostate cancer)
  • Exposure to radiation
  • Over age 60
  • High alcohol consumption
  • Obesity
  • Klinefelter’s syndrome
  • Inherited gene mutations
  • Family history of breast cancer