Breast cancer is the most common non-skin cancer among women in the United States, and the leading cause of cancer death for U.S. women aged 20–59. It is the leading cause of cancer death for women overall worldwide. Although scientists have identified many risk factors that increase a woman’s chances of developing breast cancer, they do not yet know how these risk factors work together to cause normal cells to become cancerous. Most experts agree that breast cancer is caused by a combination of genetic, hormonal, and environmental factors. The NIEHS supports animal studies to understand the role of environmental agents in the initiation and progression of breast cancer, as well as research on chemical risk factors and genetic susceptibility in human populations. In 1994, NIEHS researchers isolated a tumor-suppressor gene, BRCA1, which is known to play a critical role in the development of hereditary breast and ovarian cancer. NIEHS-funded scientists have also demonstrated that night-time exposure to artificial light can stimulate the growth of human breast tumors in mice by suppressing the levels of a key hormone called melatonin. These results might explain why female night shift workers have higher rates of breast cancer than the general population, and may offer an explanation for the rise in breast cancer incidence in industrialized countries. The NIEHS-funded Sister Study, a national study of 50,000 healthy sisters of women who have been diagnosed with breast cancer, will focus on the environmental and genetic causes of this disease.
Health Studies & Clinical Trials
What NIEHS is Doing on Breast Cancer