What Causes Breast Cancer?

This content has been reviewed and approved by

William J. Gradishar, MD FACP
Director, Breast Medical Oncology, Professor of Medicine
Robert H. Lurie Comprehensive Cancer Center
Northwestern University Feinberg School of Medicine

The exact causes of breast cancer are not known. Some women are at higher risk for breast cancer than others. But the fact is all women are at risk. That's why it is so important to follow recommendations for breast health. Early detection of problems provides the greatest possibility for successful treatment.

The risk factors associated with developing invasive breast cancer include:

• Family history, such as having a close relative (a mother or sister) with breast cancer, and genetic factors. This also includes changes in certain genes. For more information, please see the following articles: Hereditary Breast Ovarian Cancer Syndrome (BRCA1/BRCA2),  Cowden Syndrome, Li-Fraumeni Syndrome, and Peutz-Jeghers Syndrome. 
• Benign (noncancerous) breast disease 
• Previous breast biopsy in which the tissue showed a change from normal (called atypical hyperplasia) 
• Previous radiation to your breast and/or chest
• Dense breast tissue
• Menstrual periods that began early in life (beginning at 12 or younger) 
• Menopause that began later in life (55 or older) 
• Never having had children or having had your first baby after 30

Breast cancer risk may also increase due to these factors: 

• Smoking 
• Oral contraceptives
• Obesity and a high-fat diet
• Physical inactivity
• Excessive use of alcohol
• Long-term use after menopause of combined estrogen and progesterone (hormone replacement therapy, or HRT); and weight gain and obesity after menopause

Most women will have one or two risk factors for breast cancer. But most risks are so low that they do not explain the high rates of breast cancer in the population.

To learn more about breast cancer risk management and prevention, visit Breast Cancer Prevention and Risk Management.